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SOME OF THE MOST COMMON TERMS USED. In describing mushrooms it is necessary to use certain terms, and it will be incumbent upon anyone who wishes to become familiar with this part of botanical work to understand thoroughly the terms used in describing the plants.

The substance of all mushrooms is either fleshy, membranaceous, or corky. The pileus or cap is the expanded part, which may be either sessile or supported by a stem. The pileus is not made up of cellular tissue as in flowering plants, but of myriads of interwoven threads or hyphae. This structure of the pileus will become evident at once if a thin portion of the cap is placed under the microscope.

The gills or lamellæ are thin plates or membranes radiating from the stem to the margin of the cap. When they are attached squarely and firmly to the stem they are said to be adnate. If they are attached only by a part of the width of the gills, they are adnexed. Should they extend down on the stem, they are decurrent. They are free when they are not attached to the stem. Frequently the lower edge is notched at, or near, the stem and in this case they are said to be emarginate or sinuate.

Figure 2.—Small portion of a section through the spore-bearing layer of a mushroom which produces its spores on the ends of cells called basidium. (a) Spores, (b) basidium, (c) sterile cells.

In some genera the lower surface of the cap is full of pores instead of gills; in other genera the lower surface is crowded with teeth; in still others the surface is smooth, as in the Stereums. The gills, pores and teeth afford a foundation for the hymenium or fruit-bearing surface. It will be readily seen that the gills, pores and teeth simply expose in a very economical way the greatest possible spore-bearing surface.

If a section of the gills be examined by a microscope, it will be observed that upon both sides of the surface are extended hymenial layers. The hymenium consists of elongated cells or basidia (singular, basidium) more or less club-shaped. Figure 2 will show how these basidia appear on the hymenial layer when strongly magnified. It will be seen that they are placed side by side and are perpendicular to the surface of the gills. Upon each of these basidia are in some species two, usually four, slender projections upon which the spores are produced. In Figure 2 a number of sterile cells will be seen which resemble the basidia except that the latter bear four sterigmata upon which the spores rest. Among these basidia and sterile cells will frequently be seen an overgrown bladder-like sterile basidium which projects beyond the rest of the hymenium, and whose use is not as yet fully known. They are called cystidia (singular, cystidium). They are never numerous, but they are scattered over the entire surface, becoming more numerous along the edge of the gills. When they are colored, they change the appearance of the gills.

Figure 3.—Rootlike strands of mycelium of the pear-shaped puff-ball growing in rotten wood. Young puff-balls in the form of small white knots are forming on the strands. Natural size.—Longyear.

The spores are the seeds of the mushroom. They are of various sizes and shapes, with a variety of surface markings. They are very small, as fine as dust, and invisible to the naked eye, except as they are seen in masses on the grass, on the ground, or on logs, or in a spore print. It is the object of every fungus to produce spores. Some fall on the parent host or upon the ground. Others are wafted away by every rise of the wind and carried for days and finally settle down, it may be, in other states and continents from those in which they started. Millions perish because of not finding a suitable resting place. Those spores that do find a favorable resting-place, under right conditions, will begin to germinate by sending out a slender thread-like filament, or hyphæ, which at once branches out in search of food material, and which always forms a more or less felted mass, called mycelium. When first formed the hyphæ are continuous and ramify through the nourishing substratum from which there arises afterward a spore-bearing growth known as the sporocarp or young mushroom. This vegetative part of the fungus is usually hidden in the soil, or in decayed wood, or vegetable matter. In Figure 3 is a representation of the mycelium of the small pear-shaped puff-ball with a number of small white knobs marking the beginning of the puff-ball. The mycelium exposed here is very similar to the mycelium of all mushrooms.

In the pore-bearing genera the hymenium lines the vertical pores; in teeth-bearing fungi it lines the surface of each tooth, or is spread out over the smooth surface of the Stereum.

The development of the spores is quite interesting. The young basidia as seen in Figure 2 are filled with a granular protoplasm. Soon small projections, called sterigma (plural, sterigmata), make their appearance on the ends of the basidia and the protoplasm passes into them. Each projection or sterigma soon swells at its extremity into a bladder-like body, the young spore, and, as they enlarge, the protoplasm of the basidium is passed into them. When the four spores are full grown they have consumed all the protoplasm in the basidium. The spores soon separate by a transverse partition and fall off. All spores of the Hymenomycetous fungi are arranged and produced in a similar manner, with their spore-bearing surface exposed early in life by the rupture of the universal veil.

In the puff-balls the spores are arranged in the same way, but the hymenium is inclosed within an outer sack. When the spores are ripe the case is ruptured and the spores escape into the air as a dusty powder. The puff-balls, therefore, belong to the Gastromycetous fungi because its spores are inclosed in a pouch until they are matured.

Another very large group of fungi is the Ascomycetes, or sac fungi. It is very easily determined because all of its members develop their spores inside of small membranous sacs or asci. These asci are generally intermixed with slender, empty asci, or sterile cells, called paraphyses. These asci are variously shaped bodies and are known in different orders by different names, such as ascoma, apothecium, perithecium, and receptacle. The Ascomycetes often include among their numbers fungi ranging in size from microscopic one-celled plants to quite large and very beautiful specimens. To this group belong the great number of small fungi producing the various plant diseases.

In a work of this kind especial attention is naturally given to the order of Discomycetes or cup fungi. This order is very large and is so called because so many of the plants are cup shaped. These cups vary greatly in size and form; some are so small that it requires a lens to examine them; some are saucer-shaped; some are like goblets, and some resemble beakers of various shapes. The saddle fungi and morels belong to this order. Here the sac surface is often convoluted, lobed, and ridged, in order to afford a greater sac-bearing surface.

Figure 4.—Small portion of a section through the spore-bearing part of a morel in which the spores are produced in little sacs or asci. (a) An ascus, (b) an ascus discharging its spores, (c) the spores, (d) sterile cells. Highly magnified.—Longyear.

In the mushrooms, puff-balls, etc., we find the spores were borne on the ends of basidia, usually four spores on each. In this group the spores are formed in minute club-shaped sacs, known as asci (singular, ascus). These asci are long, cylindrical sacs, standing side by side, perpendicular to the fruiting surface. Figure 4 will illustrate their position together with the sterile cells on the fruiting surface of one of the morels. They usually have eight spores in each sac or ascus.

The stem of the mushroom is usually in the center of the cap, yet it may be eccentric or lateral; when it is wanting, the pileus is said to be sessile. The stem is solid when it is fleshy throughout, or hollow when it has a central cavity, or stuffed when the interior is filled with pithy substance. The stems are either fleshy or cartilaginous. When the former, it is of the same consistency as the pileus. If the latter, its consistency is always different from the pileus, resembling cartilage. The stem of the Tricholoma affords a good example of the fleshy stemmed mushroom, and that of the Marasmius illustrates the cartilaginous.