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Figure 5.--Small portion of a stem of a morel showing cell filaments. Highly magnified.—Longyear.

If the cap or stem of a mushroom is examined with a microscope of high magnifying power it will be found to be made up of a continuation of the mycelial filaments, interlaced and interwoven, branching, and the tubular filaments often delicately divided, giving the appearance of cells. Figure 5 represents a small portion of a Morel stem highly magnified showing the cell filaments. In soft fungi the mycelial threads are more loosely woven and have thin walls with fewer partitions.

The veil is a thin sheet of mycelial threads covering the gills, sometimes remaining on the stem, forming a ring or annulus. This sometimes remains for a time on the margin of the cap when it is said to be appendiculate. Sometimes it resembles a spider's web when it is called arachnoid.

The volva is a universal wrapper, surrounding the entire plant when young, but which is soon ruptured, leaving a trace in the form of scales on the cap and a sheath around the base of the stem, or breaking up into scales or a scaly ring at the base of the stem. All plants having this universal volva should be avoided, further than for the purpose of study. Care should be taken that, in their young state, they are not mistaken for puff-balls. Frequently when found in the egg state they resemble a small puff-ball. Figure 6 represents a section of an Amanita in the egg-state and also the Gemmed puff-ball. As soon as a section is made and carefully examined the structure of the inside will reveal the plant at once. There is but little danger of confusing the egg stage of an Amanita with the puff-ball, for they resemble each other only in their oval shape, and not in the least in their marking on the surface.

Figure 6.—The lefthand figure represents a vertical section through a young plant of the gemmed puff-ball showing the cellular structure of the stem-like lower half, called the subgleba. The righthand figure shows a vertical section of the egg stage of an Amanita, a very poisonous fungus which grows in woods and which might be mistaken for a young puff-ball if not cut open. The fungus forms just below the surface of the soil, finally bursting the volva, sending up a parasol mushroom. Natural size.—Longyear.

WHAT IS A FUNGUS OR A MUSHROOM? It is a cellular, flowerless plant, nourished by the mycelium which permeates the soil or other substances on which the fungus or mushroom grows. All fungi are either parasites or saprophytes which have lost their chlorophyll, and are incapable of supporting an independent existence.

There is a vast number of genera and species, and many have the parasitic habit which causes them to enter the bodies of other plants and of animals. For this reason all fungi are of economic importance, especially the microscopic forms classed under the head of Bacteria. Some recent writers are inclined to separate the Bacteria and slime-molds from the fungus group, and call them fungus animals. However this may be, they are true plants and have many of the characteristics of the fungi. They may differ from the fungi in their vegetative functions, yet they have so many things in common that I am inclined to place them under this group.

Many, such as the yeast fungus, the various fermentative fungi, and the Bacteria concerned in the process of decomposition, are indeed very useful. The enrichment and preparation of soils for the uses of higher plants, effected by Bacteria, are very important services.

Parasites derive their nourishment from living plants and animals. They are so constituted that when their nourishing threads come within range of the living plant they answer a certain impulse by sending out special threads, enveloping the host and absorbing nutrition. Saprophitic plants do not experience this reaction from the living plants. They are compelled to get their nourishment from decaying products of plants or animals, consequently they live in rich ground or leaf mold, on decayed wood, or on dung. Parasites are usually small, being limited by their host. Saprophytes are not thus limited for food supply and it is possible to build up large plants such as the common mushroom group, puff-balls, etc.

The spores are the seeds or reproductive bodies of the mushroom. They are very fine, and invisible to the naked eye except when collected together in great masses. Underneath mushrooms, frequently, the grass or wood will be white or plainly discolored from the spores. The hymenium is the surface or part of the plant which bears the spores. The hymenophore is the part which supports the hymenium.

In the common mushroom, and in fact many others, the spores develop on a certain club-like cell, called basidium (plural, basidia), on each of which four spores usually develop. In morels these cells are elongated into cylindrical membranous sacs called asci, in each of which eight spores are usually developed. The spores will be found of various colors, shapes, and sizes, a fact which will be of great assistance to the student in locating strange species and genera. In germination the spores send out slender threads which Botanists call mycelium, but which common readers know as spawn.

The method and place of spore development furnish a basis for the classification of fungi. The best way to acquire a thorough knowledge of both our edible and poisonous mushrooms is to study them in the light of the primary characters employed in their classification and their natural relation to each other.

There is a wide difference of opinion as to the classification of mushrooms. Perhaps the most simple and satisfactory is that of Underwood and Cook. They arrange them under six groups:

1 Basidiomycetes—those in which the spores or reproductive bodies are naked or external as shown in illustration 2 on page 15.

2 Ascomycetes—those in which the spores are inclosed in sacs or asci. These sacs are very clearly represented in illustration Figure 4 on page 18. This will include the Morels, Pezizæ, Pyrenomycetes, Tuberaceæ, Sphairiacei, etc.

3 Physcomycetes—including the Mucorini, Saprolegniaceæ, and Peronosporeæ. Potato rot and downy mildew on grape vines belong to this family.

4 Myxomycetes—Slime moulds.

5 Saccharomycetes—Yeast fungi.

6 Schizomycetes—are minute, unicellular Protophytes which reproduce mainly by transverse fission.