To the Fun Science Gallery Contents

 

3 - Lower Plants (Cryptogams)

Giorgio Carboni, March 2007
Translated by Sarah Pogue

 


Figure 1 - Rhizomnium punctatum (moss). (Photo G.P. Sini).

CONTENTS
INTRODUCTION
METAGENESIS
CRYPTOGAMS
Mosses
Liverworts
Ferns
Fungi and Moulds
Lichens
IN DEPTH
CONCLUSION
BIBLIOGRAPHY
INTERNET RESOURCES


INTRODUCTION

In this article, we will look at plants with relatively primitive characteristics that are also known as “inferior” plants. These, in fact, do not possess true roots, stems, leaves and other specialised organs that characterise the “superior” plants. These plants do not have flowers and are called Cryptogams to indicate that their reproductive organs are hidden. Notwithstanding these characteristics, these plants are of great interest due to their form and the solutions that they have adopted in order to reproduce and survive.


METAGENESIS

Even though the inferior organisms reproduce via asexual reproduction, it is rare for sexual reproduction not to take place at least occasionally. In order to reproduce sexually, the parents must unite their chromosomes in a single cell and this occurs by means of fertilisation. Every parent supplies its chromosomes which are haploid, thus the fertilised cell has a double supply of chromosomes and so is diploid. The fusion of the gametes is called fertilisation and gives birth to a cell called a zygote from which the adult organism develops. Sexual reproduction has the advantage that it makes two copies of every gene available to the organism, compensating for any eventual defects in one of the copies. Furthermore, it has the advantage that it results in a mixing of the genes and so favours greater variation within the species.

The number of chromosomes in the haploid cell is indicated by the letter "n", while the number of chromosomes in diploid cells is indicated by "2n". In humans, n = 23, which means that the haploid cell contains 23 chromosomes, while the diploid number is 46. Normally, the chromosomes are “dispersed” in the nucleus and are not visible. During cell division, the chromosomes condense and unite in homologous pairs according to size, type and the succession of genes that they contain. At this point, the chromosomes assume the aspect of an "X" and become visible under the microscope. Normally, organisms produce haploid gametes but as we will see the adult organisms are not always diploid.

There are two types of cell division: mitosis and meiosis. Mitosis replicates the chromosomes in the cell nucleus forming two identical sets and so from a 2n cell two 2n cells are produced, or from an n cell two n cells result. With meiosis, instead, there is "reductional" division, in the sense that from a 2n parent cell two n cells are produced. Meiosis is also preceded by an exchange of genes between homologous chromosomes. This reduction in the number of chromosomes to the haploid condition is important to avoid a doubling of the chromosome number at every generation, a situation which, in a short amount of time, could become unmanageable for the cell. Mitosis is generally linked to the growth of the organism or to its asexual reproduction whilst meiosis is connected to sexual reproduction.

 

 

Except in rare cases, all organisms undergo sexual reproduction, even though for some it is systematic and for others only occasional. Therefore, during the life cycle, almost all organisms pass alternately from the haploid to the diploid condition. For example, bacteria and protists spend their existence almost exclusively in the haploid state. They reproduce sexually only occasionally giving rise to a diploid organism which, however, after a brief period undergoes meiosis producing individuals that are haploid. In the multicellular algae, the bryophytes and the ferns, there are sporophytes (diploid) that produce spores (haploid) which are capable of germinating. From these spores a gametophyte (haploid) originates which then produces male and female gametes. In certain cases (ferns), the sporophyte is larger than the gametophyte, in others (mosses) it is the gametophyte that is the larger of the two, and in others these two forms are of similar size. In the past, the morphological difference between the sporophyte and the gametophyte caused specimens that belonged to the same species to be attributed to different species. In humans, as in all vertebrates, the diploid condition occupies almost the entire life cycle and it is only just before fertilisation that the haploid gametes are produced. In the superior plants, the sporophytes (the true plant) prevail, whilst the gametophytes are reduced to grains of pollen and ovules. Therefore, in the course of evolution, there has been a departure from organisms that were haploid for almost all of their life cycle towards organisms such as the superior plants and animals that pass almost all of their life cycle as diploid organisms.

This biological cycle, in which diploid generations alternate with haploid generations, is called metagenesis. It is important to keep this process in mind if you want to follow the various phases of sexual reproduction of the inferior plants and if you want to identify and observe the plant structures under the microscope.


CRYPTOGAMS

As you know, the first forms of life were born in the sea approximately 4 billion years ago and only a few hundred million years ago the plants and animals began to colonise the land by means of a long evolutionary process. Within the cryptogams we can observe the passage from the acquatic to the terrestrial environment and in their reproductive cycles they are still very linked to water. The Cryptogams do not possess the specialised structures of the superior plants such as roots, stems, branches, leaves and flowers. Their little differentiated structure is called the thallus and amongst the thallophytes we find the algae, fungi, lichens, mosses and liverworts. In contrast to the superior plants, which reproduce by means of flowers and seeds, the cryptogams reproduce using spores or by vegetative and asexual means.

With the exception of the ferns, the cryptogams do not possess a vascular system for the transport of fluids. In general, they do not have a cuticle, the waxy layer that protects the plant from water loss through evaporation, and this is indicative of their aquatic origin and of the necessity of such plants to live in shaded humid environments. Even during their reproductive cycle the cryptogams need water as the male gametes swim in this element to reach the female gametes. The cryptogams that live on the land still need a veil of water to cover them during the reproductive period. For the plants, the passage from the aquatic environment to dry land has led to the development of roots to absorb water from the soil, of a stem and branches to raise the plant from the earth and of leaves to stretch out their photosynthetic apparatus which previously floated in the water. This passage has also led to numerous other adaptations to the particular conditions of the different ecosystems. Many cryptogams have instead remained very similar to their ancestors of a hundred million years ago.

 

TERMINOLOGY
The term "Cryptogamae" (from the Greek: cripto and gàmos = hidden marriage) indicates plants deprived of visible reproductive organs (i.e. without flowers). It contrasts with the term: "Phanerogamae" (visible marriage), which indicates plants with evident reproductive organs (flowers). The term Cryptogam does not include plants which are homogenous from an evolutionary point of view, but includes organisms that belong to different kingdoms. Organisms that are not animals and which do not possess flowers can be considered to be Cryptogams: bacteria, algae, fungi, lichens, mosses, peat mosses (sphagnum), hornworts, liverworts and ferns. Often, this broad interpretation of the term is used for convenience, but keep in mind the fact that the bacteria and fungi are part of autonomous kingdoms. The same is partly true also for the lichens which are a symbiotic association between a fungus and a unicellular alga.

The term "Bryophyte" (from the Greek: bryon = moss) indicates plants of small size without a vascular system and includes: mosses, peat mosses, hornworts and liverworts. In turn, the term “Thallophyte" indicates plants that do not possess true roots, stems and leaves. This group includes the multicellular algae, the fungi, the lichens and the bryophytes, but does not include the ferns. The term "Cormophyte” is in contrast to this, these are plants which have the "corm", that is the structure composed of roots, stem and leaves. The phanerogams and the ferns are found amongst the cormophytes.

In this article, we will deal with the plants mentioned in the contents and, within these limits, those belonging to the Cryptogams.


MOSSES

The mosses are small plants that live in damp shaded areas. Their humble aspect leads us to ignore them, however they present different aspects which are certainly very interesting for microscopy enthusiasts. Before laying a hand on the microscope, it is a good idea to examine the life cycle of this organism so as to better understand that which we observe.

The life cycle of the mosses begins with the liberation of the spores from the capsule which opens when the operculum is shed (Figure 3). The spore is capable of germinating and from this a gametophyte develops (the plant that we call moss). When it is mature, the gametophyte (n) produces flagellated sperm cells from a structure called the antheridium and egg cells in a structure called the archegonium. The sperm cells go in search of the archegonium and to do this it is necessary to have sufficient humidity to envelop the plant in a veil of water. The fertilised egg cell, or zygote (2n), matures and develops whilst remaining attached to the gametophyte. This plant takes the name of sporophyte (2n) and is formed of a filament terminating in a capsule containing the spores (n). In certain species, the antheridium and archegonium are present on separate plants (dioecious species). Human beings are also dioecious organisms since the gametes are produced by different sporophytes: man and woman.

 

 

Therefore, in the mosses the gametophyte (and not the sporophyte) is the larger organism, the plant that we call moss. The sporophyte is formed of a capsule containing the spores and the filament that sustains it. As you can ascertain, the sporophyte is attached to the gametophyte by means of a foot.

 

Figure 4 – Pot with moss and liverworts.

Figure 5 – Moss plant.
Field = 10 mm ca.

Figure 6 – Moss leaf cells. The chloroplasts are clearly visible.

 

Take a moss plant and wash it under running water. Examine the leaves and the rhizoids (roots) under the stereoscopic microscope. In general, the leaves of the mosses are formed of a single layer of cells. Pick off some leaves and place them between the slides with a little water. Observing them with the biological microscope, it will be possible to see the chloroplasts which adhere to the internal surface of the cell, so you can focus alternately on the superior and inferior layers of the chloroplasts. The rhizoids are not true roots but long cells or filaments of cells. Try to find any walls that separate the cells. Examine the foot, filament, capsule, operculum and spores of the sporophyte. Try to make the spores germinate by placing them in fine soil that has been sterilised in the oven. Try also to identify the archegonium and the antheridium in the fronds. Note the absence of the stem and branches, and the absence of the stomata and vascular tissues in the leaves.

Examining the soil, it will be easy to recognise the different species of moss. For example, those in Figures 4, 5 and 6 have relatively large leaves. There are others with very small leaves and with a slightly “bushy” aspect. On concrete walls and on humid seldom used footpaths it is easy to encounter masses of compact mosses, intense green in colour and with a velvet appearance. For every species, the leaves, the cells and the other structures will be different. Therefore, for each species that you encounter, examine the entire organism and the individual parts. At times, there are small animals present on the plant. Compile a file on each species complete with photographs.


LIVERWORTS

The liverworts are present in leafy/scaly forms (indication of fronds) or in thallose forms (tongue/thallus that adhere to the ground). Their life cycle is fairly similar to that of the mosses and the frond or thallus is the gametophyte (n). The archegonia and the antheridia form on the margin or apex of the thallus. In Marchantia, however, these are carried on an umbrella-shaped structure (archegoniophores and antheridiophores) which are part of the gametophyte. The spores are produced near the archegonium. The liverworts also reproduce vegetatively by means of propagules with a discoidal form (Figures 11 and 12). In the Marchantia the propagules are produced in circular cups, while in the Lunularia the cups are in the shape of small moons (Figure 11).

Even though liverworts are not very striking plants and are often little considered due to their humble appearance, under the microscope they will amaze you. Take a specimen of Lunularia cruciata, an easy to find liverwort around fountains, waterfalls, streams and in other wet but not submerged areas. If you cannot find it in nature, go to a garden centre where pot plants are sold. As you can see in Figure 7, this liverwort has the aspect of tongues that adhere to the soil and which are approximately 1cm in width and 2 or 3 cm in length. Detach one and examine the upper and lower surfaces under the stereoscopic microscope where you will see the pseudoroots, called rhizoids, which arise directly from the tongues.

 

Figure 7 – Liverwort thalli (Lunularia cruciata).

Figure 8 – Liverwort thallus
overturned to show the rhizoids.

Figure 9 – Rhizoids of Lunularia cruciata.

 

Under the biological microscope, the rhizoids appear as long unicellular filaments or filaments composed of many cells in a row. It will be possible to distinguish at least two types of fibre: one smooth and the other “grainy” (Figure 9). Under a higher magnification, the grainy fibres have a disconcerting aspect, that of a small tube with spines turned inwards (Figure 10), the function of which it is difficult to comprehend.

 

Figure 10 – “Grainy” rhizoids of
Lunularia cruciata. Diameter = 0.2 mm.

Figure 11 – Thalli of Lunularia cruciata
and cup with propagules.

Figure 12 – Propagules about to disperse.
Diameter = 0.5 mm.

 

Returning to examine the thallus with the stereoscopic microscope, in autumn and winter it will be easy to discern small cups containing green discs. These are the propagules (Figures 11 and 12), a sort of small spontaneous offshoot with which the plant reproduces vegetatively. In these species, the cups are in the shape of small moons. Upon careful observation of the thallus, you will notice that it is dotted with pale spots. Increasing the magnification, you will see a "tile" pattern (Figure 13). The first thing that comes to mind is that each "tile" corresponds to a cell, but this is not so. Each of those polygonal forms defines a chamber composed of hundreds of cells. In Figure 14, a transverse section of the leaf of Lunularia is shown where you can see an inferior layer of cells void of chloroplasts, an intermediate layer rich in chloroplasts and an upper layer again without chloroplasts. In this upper layer the pore through which the gas exchange necessary for photosynthesis takes place is clearly visible. This pore is not capable of regulating its opening and so it remains constant. As I have already said, beneath the pore there is a spongy layer of photosynthetic cells in which the chloroplasts are visible. The upper epidermic layer is transparent and allows light to pass to the photosynthetic layer. The photosynthetic cells are also visible from above by transparency and in Figure 13 have a fine grainy appearance.

 

Figure 13 – Polygonal structure of Lunularia.
Average distance between the pores = 0.4 mm.

Figure 14 – Section of the photosynthetic chamber of
Lunularia.
Note the intermediate layer of cells
with chloroplasts and the overlying pore

Figure 15 - Marchantia polymorpha.
(Photo G.P. Sini).

 

With very fine tweezers, try to remove the upper layer of one of the chambers to reveal the photosynthetic layer and observe it with both microscopes. Utilise both transparent and reflective illumination. Immersing a leaf in water, in a few minutes you will see an air bubble form in correspondence to each pore. In all probability this is oxygen: the “waste” product of chlorophyll photosynthesis. In order to observe the sperm cells, in spring crush the thallus of a liverwort and try to make a drop of the resulting fluid fall onto a microscope slide, add water and cover. The sperm cells should appear as flagellated cells.

Gather other liverworts and examine their general structure and the photosynthetic chambers by making thin sections of the thallus. Observe and describe the different types of rhizoid. Try to determine if these are formed of filaments composed of only one cell or a sequence of cells. Describe the structure of the different species. Try to plant propagules in a small nursery constructed specifically for this purpose and place it in a humid, cool and shaded spot. The containers must allow rainwater to drain. Maintain the substrate humid and cover the nursery with a sheet of glass.


FERNS

The ferns are cryptogams which are closer to the phanerogams from an evolutionary perspective, such that it is thought that there is a relationship of parentage between the former and the latter. Like the phanerogams, many ferns possess a cormoid structure (composed of roots, stem and leaves), vascular tissues, external cuticle etc. They do not however possess flowers or seeds, but reproduce by means of spores, and for this reason they are grouped with the cryptogams. The fronds are equipped with stomata and spongy photosynthetic tissues. The ferns can display a wide variety of forms, for example the Lycopodium clavatum (wolf paw clubmoss), the Maidenhair Fern, Equisetum species (horsetails) and Selaginella species (spikemosses). Despite the similarity of the Selaginella species to the phanerogams, many scholars do not consider them to be ferns, whilst others do count them as ferns due to the fact that these plants do not produce seeds but spores.

 

 

With reference to the Figure 16, we can have the life cycle of the ferns begin with the liberation of the spores (n) from the mature sporangia. These spores are able to germinate and to produce a prothallus (n), a sort of leaf in the form of a heart which, other than rhizoids, also carries the archegonia and the antheridia. This leaf is the gametophyte (n) while the sporophyte (2n) is the leafy organism that we all know, but lets proceed with the life cycle. In the appropriate season and under suitable conditions, the antheridia open and the flagellated sperm cells swim in the veil of water that covers the plant during the rainy or humid season, directing themselves towards the archegonium to fertilise the egg cells. From the fertilised egg cell (zygote, 2n) the sporophyte develops (2n) which grows on the gametophyte. When the young sporophyte is well anchored in the soil, the gametophyte dissolves. When mature, the sporophyte produces sporangia in groups called sori on the undersurface of the leaves. In the interior of each sporangium the mother cells (2n) undergo meiosis and are transformed into spores (n). When the sporangium is mature, it opens releasing the spores which are ready to germinate, and the cycle begins again.

The archegonium of the ferns is similar to that of the mosses and has the form of a hip flask. Each archegonium contains an egg cell or oosphere. While the moss plant is a gametophyte, the fern plant is a sporopyte. The ferns represent an important evolutionary step for the plants in the passage from the gametophyte to the sporophyte as the prevalent form.

 

Figure 17 – Maidenhair fern (Adiantum capillus Veneris).

Figure 18 - Sori (covered by the indusium) on the
under surface of the fronds of the Maidenhair fern.
Diameter of the indusia: circa 2 mm.

Figure 19 - Sporangia with a removed indusium.
Diameter of the sporangi: circa 0.2 mm.

 

The maidenhair fern (Adiantum capillus Veneris), Figure 17, is a beautiful fern that loves to be sprayed with water and to have a shaded exposure. It is often found at the base of waterfalls, but it is easier to find in garden centres. This fern is very suitable for observation of the fronds and the reproductive organs. Observe the sections of the leaves and the thin black stems. Examine also the roots (in contrast to the fungi, the mosses and the liverworts, the ferns have true roots).

Collect some fern fronds and try to locate the sporangia on the underside. Normally, these sporangia are grouped together in sori (groups) and these sori are often covered with a film called the indusium (Figure 18). When the fern is mature, the indusium shrivels up and the sporangia open to release the spores. If, however, the sori are still covered by the indusium, remove it and observe the sporangia with a stereoscopic microscope. If you use a spotlight concentrated on the sporangia, you can see the explosion of the sporangia and the liberation of the spores. If this does not happen, open some sporangia to obtain the mother cells or the spores and observe them at a higher magnification. Examine the surface of the fronds to find the stomata. Make a transverse section of a frond to observe the cells, the tissues and the vascular tissue. Make a transverse section of a stem to observe the type and placement of the vascular vessels. Remove some roots and examine them.

In a garden centre, procure a Selaginella fern (Figure 20). This is quite a highly evolved fern, rich in scaly leaves arranged in an orderly way, of which one part is larger than the others. Between the stem and leaves there is a ligule which fulfils the role of absorbing water. The leaves have a central veining with trachee and along this veining the stomata are visible. There are at least two types of leaf cell: one on the upper surface of the leaf with an approximately square shape which has a large central chloroplast and a zig-zagging membrane, and another type on the undersurface of the leaf, rectangular in shape and with a wavy membrane. From the lower fronds the temporary roots arise. At the apex of the branches sporophylls can be present, small spikes that bear the reproductive
organs and spores.

 

Figure 20 - Fronds of Selaginella.

Figure 21 – Leaf cells of Selaginella.

Figure 22 – Stomate on the leaf of Selaginella.

 

At the beginning of spring, shake the stalk of Equisetum (or horsetail, Figure 23) and collect the spores. Lay some on a microscope slide without covering it. Under the microscope, the spores appear to endowed with four filamentous arms (Figure 24). Breathing on these, the filaments contract (Figure 25).

 

Figure 23 – Equisetum (horsetail) sporophyte in spring (Equisetum arvense L.) Figure 24 – Spread out spores of Equisetum.
(Photo G.P. Sini)
Figure 25 – Contracted spores of Equisetum.
(Photo G.P. Sini)

 

Where can you collect ferns? Search in shaded, cool, humid places such as in the woods or close to streams, springs or waterfalls. Otherwise, go to a garden centre where you can easily find several species.

 

FERN REPRODUCTION
Fern propagation can have many objectives: to obtain new plants, to follow their life cycle and in particular to allow the examination of the prothalli, which are otherwise difficult to find in nature. According to the species, ferns can be propagated by dividing the root tufts, by separating the stolons or by means of the propagules, but these methods of vegetative propagation do not allow us to study the life cycle of the plant. Therefore, we will adopt the method of reproducing from the spores.

- Between June and September, collect healthy fronds and place them on sheets of white paper or even on newspaper. After a week, collect the spores in an envelope and put this in a dry place. The seeding can be done immediately or the following spring.
- Sterilise a large shallow seed tray with bleach or boiling water or in the oven (200°C for 30 minutes).
- Lay a 1.5-2 cm layer of washed gravel on the bottom of the tray.
- Prepare the compost as follows: 7 parts soil; 2 parts peat; 2 parts fine sand; 2 parts decomposed leaves or grass (or some powdered fertiliser).
- Sterilise the compost in the oven (200°C for 30 minutes).
- Mix and then sieve the compost through a sieve with holes of 12 mm.
- Place a layer of the sifted compost not deeper than 2.5 cm on top of the gravel.
- Place 1,5 - 2 cm of the sifted compost
- With a plank of wood, level the compost by pressing on it gently.
- Mix the spores with a handful of the sifted sterilised soil.
- Scatter this mixture evenly over the compost in the seeding tray.
- Cover the tray with a sheet of glass, leaving several centimetres of air underneath.
- Place the tray in a shaded, humid and cool location.
- Every so often, wet the tray from underneath. Do not allow it to dry out too much.
- Within 1 – 3 months, many prothalli should appear.
- From this moment onwards, the plants should be watered with a fine rain using a watering can and preferably using rainwater in order to allow the sperm cells to reach the archegonia.
- Within 6 months, the prothalli should become small plants which sometimes have the shape of a heart.
- Within 9 months, the sporophytes should develop on the gametophytes (the young ferns).
- Progressively raise the glass and remove it after 3 weeks.
- When the plants have developed the fronds, transfer them to progressively larger vases to make the roots and fronds toughen up.
- In the autumn and spring, transplant the ferns into the garden or in nature.

The phase that most interests us is from the moment in which the prothallus appears until the birth of the sporophyte. In particular, we will search for the reproductive organs on the prothallus. It will be somewhat difficult to observe the sperm cells of the fern, but you can always try. It should be easier to observe the archegonia with the egg cell, the rhizoids and prothallus.
 

 

FUNGI AND MOULDS

Due to the fact that the fungi are more primitive than the mosses, liverworts and ferns, in the lists of the cryptogams they are usually indicated at the beginning. Here, instead, I have placed them at the end because with their particular coenocytic cellular structure (cells which contain many isolated nuclei), they could have created some confusion with the concepts of haploid and diploid just introduced. Consequently, I have also placed the lichens at the end.

The principal characteristic of the fungi is that they do not possess chloroplasts and therefore are not capable of photosynthesis. For nourishment, they depend on other organisms of which they can be parasites or symbionts, or they nourish themselves on decomposing organic substances (saprophytic fungi). Together with the bacteria, the fungi are the principal decomposers of organic substances and therefore play a very important role from the environmental point of view. The fungi are composed of multicellular filaments called hyphae which together compose the mycelium. Some species produce a fruiting body, which is commonly called the fungus, an organ specialised in the production of spores. Many other species, instead, do not produce a fruiting body. These are considered to be inferior fungi and are more commonly known as moulds. The sexual reproduction of the fungi can take place as a result of the fusion of the gametes, fusion of the gametangia or by fusion of the non-specialised hyphae. Normally, the fusion of the hyphae is not immediately followed by the fusion of the nuclei, therefore the cells of many fungi have 2 nuclei (dikaryotic) which can combine even after a long time.

The kingdom of the fungi is subdivided as follows: Zygomycota, Ascomycota, Basidiomycota, Deuteromycota. The Zygomycota are composed of only a few hundred species, the best known of which is the black bread mould. The Ascomycota have their spores closed in small sacs (asci). The hyphae have septa but the cells contain only one nucleus. The single-celled ascomycota are called yeasts. These nourish themselves with sugary substances by means of a process called fermentation. The truffles are also included amongst the Ascomycota. To the Basidiomycota belong almost all of the species that produce a fruiting body. They are formed of a vast mycelium that produces the fruiting body. The spores germinate giving life to the monokaryotic (n) mycelia. From the fusion of hyphae from different stumps dikaryotic mycelia are formed (n + n). When these spread out, they produce a fruiting body under whose cap the reproductive structures called basidia form. In contrast to the asci which produce spores in their interior, the basidia produce them on their exterior. In the basidia the fusion of the nuclei (2n) takes place followed by meiosis, the formation of the spores (n) and their propagation. Amongst the Deuteromycota sexual reproduction is not known. Amongst the 25,000 species there are those which are parasites of plants and animals (thrush, athlete’s foot etc.). Some are used in the production of cheese, antibiotics and medicines. This is the group richest in moulds, although the other groups also contain moulds.

Collect the mature fungi to observe the gills (lamellae) or the spongy tissue under the cap and the basidia. Often it is possible to see small insects that feed on the spores. On the stem, you can observe insect larvae which you can place in a container in order to see the adult that they turn into. Lay the cap of a fungus on a microscope slide. The next day, you will be able to see many spores (Figure 28) laid out in rows like the gills of the fungus (Figure 27). The fruiting bodies of the fungi can vary widely in form and often have a very attractive appearance, but given their dimensions they are not suitable for observation under the microscope, except for the basidia, basidiospores, ascospores and any small animals that feed on the spores or on the tissues of the fungus. The “moulds” are much more suitable for microscopic observations.

 

Figure 26 – Basidiomycota fungus.

Figure 27 – Spores on a microscope slide.

Figure 28 – Fungal spores (circa 400 X).

 

To begin, look for moulds in old jam jars or in tomato purée jars. Otherwise, you can prepare a culture. For this purpose, cut a slice of tomato or of another fruit or vegetable and place it in a shallow glass dish. Leave the dish uncovered for an hour to allow it to collect spores and then place it in the fridge. If necessary, add some drops of water to keep the environment humid. After a week or two, it should be possible to observe the mould. Cover the dish with a lid to retain the humidity and leave the mould to grow a little. In this way, you will have a humidity chamber.

Every so often, with a stereoscopic microscope, examine the culture. When you observe the presence of spores amongst the hyphae, use the stereoscopic microscope and a thin needle to take a sample of mycelium. The best part of the mould is at the edges where it grows actively and where the spores are found. These samples should not be bigger than 2 - 3 mm2. Place these samples on a microscope slide where you have already put several drops of water. With a second needle, try to arrange the filaments so that they are spread out.

Normally, the water cannot penetrate between the fibres and large air bubbles can impede observation. The situation will improve if you substitute the water with alcohol. Try also to use distilled water with an added surfactant such as those used to prevent the formation of drops on photographic film as it dries. You can also try using washing-up liquid. Surfactants lower the surface tension of the water and favour the soaking of the surfaces with which it comes into contact. The amount of surfactant used must be minimal, otherwise the membranes of the hyphae will be destroyed. The objective is to have the fibres spread out sufficiently to avoid excessive overlapping and to allow their easy examination. Finally, mount the coverslip.

 

Figure 29 – Mould on tomato purée.
Diameter 6 mm.

Figure 30 – Mould spores (circa 400 X).

Figure 31 – Hyphae of Gorgonzola mould (circa 400 X).

 

Another method for observing moulds and their spores consists in spreading a thin layer of jam in the centre of a microscope slide. In a Petri dish, place a sheet of very damp absorbent paper and on top of this place the slide. Leave it exposed to the air for a while so that the spores can deposit there and then cover the dish and put it in the fridge. After approximately 10 days, you should have a slide ready to observe under the microscope without having to sample the hyphae, a process which, as you have seen, is rather demanding.

When, after many inevitable attempts, you succeed in obtaining decent preparations, you can observe the hyphae, the spore-bearing structures (sporangia) and the spores themselves (Figure 30). The spores are produced in great numbers by mitosis of the cells of the sporangium. From the form of the hyphae and above all from that of the sporangium it is possible to identify the mould species. To observe the nuclei, it is necessary to colour the hyphae.

Another method used principally for collecting moulds in domestic environments, for example from the walls, is that of pressing a strip of adhesive tape gently on top of the mould which can then be mounted on a microscope slide.

Amongst the Internet resources that I have listed at the end of this article, you can find detailed information on the moulds and on the techniques for their cultivation, observation and identification.


LICHENS

The lichens are a symbiotic association of a fungus and an unicellular alga. Usually, the alga is a green alga or a cyanobacterium, the fungus however is almost always an ascomycota. While the fungi need to find organic substances in the soil, the lichens need only air, water, light and some mineral salts. In fact, the alga supplies the fungus with the organic substances it needs and the fungus returns the favour by supplying the alga with mineral salts. The fungi are in fact very efficient in absorbing inorganic compounds from the soil. The algae and the fungi of the lichens can also live separately, but from their collaboration new and very resistant individuals are born which can survive long periods of desiccation. The resistance and the adaptive capacity of the lichens is such that they can survive in environments so hostile that no other plant life is able to colonise them. The lichens can live on many substrates, but you can find them most easily on the branches and bark of trees, on stones and on concrete walls

Generally, the thallus of the lichens is distinguished as crustose, foliose or fruticose. The foliose lichens are subdivided into homomeric and heteromeric. The homomeric thallus does not have distinct layers, but is composed of hyphae in which the algae are distributed in a homogenous manner. The heteromeric thallus is typically composed of 4 layers (Figure 34). The superior cortex is formed of tightly interlaced hyphae; the medulla is a thick layer of fibres with the consistency of felt in which air can circulate; usually under the superior cortex there is a layer of algae (gonidial layer); the inferior cortex is also composed of tightly interlaced hyphae and is often in contact with the substrate by means of rhizines.

That the lichens are the result of a strange marriage is proven by the fact that the algae do not reproduce sexually, but only through mitosis, while the fungus continues to reproduce as though it lived alone. On the lichens it is often possible to discern numerous structures in the shape of small bowls (apothecia), whose internal tissue (hymenium) is rich in asci (small sacs) containing ascospores (n), able to give life to a new mycelium. Encountering a suitable alga, this mycelium can generate another lichen. The lichens also reproduce vegetatively following the detachment of a piece of its tissue. Some lichens develop small column-like appendages or miniscule balls of hyphae and algae ready to detach themselves at the smallest stimulus to give life to a new colony.

 

Figure 32 – “Yellow-green” lichens (Xanthoria sp.). The
 numerous apothecia cover the thallus almost entirely.

Figure 33 – “Blue-green” lichens.

Figure 34 – Transverse section of a Xanthoria
thallus. Note the superior cortex, the medulla,
the gonidial layer and the inferior cortex.
Field = 0.34 mm.

 

During a humid period, or better still during a rainy period, collect some lichens and examine them under the stereoscopic microscope. Their attractive structure will not fail to impress you. Again with the help of a stereoscopic microscope, using a needle take a fragment of cortex. You should see the green colour of the algae, but these algae are so small that even at a magnification of 50X you will only be able to see them as small dots. Place the fragment on its side and try to see the narrow width of the upper layer of hyphae and the even thinner layer of algae. Dig a little in the underlying layer until you reach the substrate.

 

 

Figure 35 – Superior cortex, medulla and algae
of a lichen (Xanthoria sp).
Field = 0.12 mm. Lomo objective 65X water imm.
Figure 36 – Section of hymenium with asci.
Field = 0.34 mm.
Figure 37 - Ascospores.
L ~ 16 μ. Field = 0.12 mm.
Lomo objective 65X water imm.

 

Now, try to collect small fragments of lichen from the intermediate layer in order to observe the algae and place them on a microscope slide. Add a few drops of water and cover. Under the biological microscope, these algae appear as small spheres bright green in colour lying in the middle of colourless or white hyphae (Figures 34 and 35). Again with the use of a needle, collect some fragments of the hymenium. Observing them at a high magnification, you can see the asci containing the ascospores (Figure 36). Collect at least 10 fragments as only some will release ascospores (Figure 37).

Take a sample of lichen and make transverse sections. With the biological microscope, observe the structure of the 4 layers of the thallus (Figure 34) and observe also the hyphae and the algae (Figures 34 and 35). In a transverse section of the apothecium, you can also see the asci with the ascospores (Figures 36 and 37).


IN DEPTH

While you carry out the various observations under the microscope, study in a highschool biology textbook (for example: [001] or [002]) the subjects indicated below. You can also use guides, atlases and any other texts that are useful to you:

The conquest of dry land by the plants. Photosynthesis and respiration. Feeding and energy. The carbon cycle. The life cycle of organisms in general (metagenesis). The life cycle of: bacteria, protozoans, unicellular algae, mosses, ferns, fungi, gymnosperms, angiosperms, vertebrates. The inferior plants (their divisions, principal characteristics and reproduction).


CONCLUSION

Once again you can realise the enormous potential of the exploration, observation and experimentation that can be undertaken for each of the organisms that I have merely introduced. Every class, order, family, genus and species will reveal itself to be so different from the others that your research will be practically infinite. Those few examples that I have presented serve only as a beginning and must not be interpreted as observations to be carried out without going any further. Instead, they must be seen as a point of departure for numerous other explorations that will not fail to fascinate you.


BIBLIOGRAPHY


 

301

Ferns, mosses & lichens of Britain, Northern & Central Europe; Collins photo guide
An excellent guide to the Ferns, Mosses and Lichens. Correct presentation of the general characteristics and clear indications for the identification of the species.

302

 

303

Ruzin, S.; Plant Microtechnique and Microscopy; Oxford University Press Inc, USA 1999,57 figs, 334 pp.
A superb modern reference book, full of practical information, well written and designed, but of limited use to the amateur microscopist.

304

Boedijn K.B.; The Lower Plants; Thames & Hudson London 1968; 312 pages with 157 colour and 383 b/w illustrations.

305

 

306

 

Look also at Internet works and references of general character which are indicated in the presentation article of this guide.

 


INTERNET RESOURCES

3001 -
3002 - http://scitec.uwichill.edu.bb/bcs/bl14apl/bryo1.htm  The Bryophytes
3003 - http://www.britishbryologicalsociety.org.uk/  British Bryological Society
3004 -
3005 - http://www.smsi.org/publications/mn5001-4.shtml  The Use of the Microscope in the Study of Mosses
3006 - http://www.mushroomexpert.com/microscope.html Using a Microscope to Study Mushrooms
3007 - http://www.backyardnature.net/mosses.htm  Mosses
3008 - http://www.gnps.org/Massie.htm  Creating a moss garden
3009 - http://rbg-web2.rbge.org.uk/bbs/Resources/Fletcher.pdf  Moss Grower's Handbook
3010 - http://worldofmosses.com/other/links.html  Links to other sites about moss
3011 -
3012 -
3013 -
3014 - http://helios.bto.ed.ac.uk/bto/FungalBiology/index.htm  Fungal Biology
3015 - http://www.botany.utoronto.ca/ResearchLabs/MallochLab/Malloch/Moulds/Moulds.html  Moulds. Look also at the other pages
3016 - http://www.botany.utoronto.ca/ResearchLabs/MallochLab/Malloch/Moulds/Examination.html  Moulds under the Microscope
3017 -
3018 -
3019 - http://www.microscopy-uk.org.uk/mag/artmar04/jbbotany2.html Botanical Microtechnique Part 2. Staining Botanical Sections. Very interesting also for the bibliography.

Internet keywords: cryptogams, mosses, liverworts, ferns, fungi, lichens, bryophyte links, fern links, mosses links, moulds links, botanical microtechnique.


 


Send your opinion on the article

zz_writer.gif


To the other articles  To the top of the article