417 



STRUCTURE 



Let us now examine a little more closely the structure of a mature 

 mushroom of the umbrella type. We find that it consists of a stem, 

 or stipe, and an expanded portion which is called the cap, or pileus. 

 If our mushroom happens to be an Amanita it will have also a cup- 

 like structure, or volva, at the base of the stem, and a ring, or annulus, 

 farther up on the stem. There are some kinds of mushrooms which 

 have a volva but no ring, others which have a ring but no volva, and 

 many which have no ring and no volva. Also the character of these 

 structures, when present, differs greatly in different kinds of mush- 

 rooms. The ring may be very large and thick and conspicuous, or 

 \ery small, delicate, and inconspicuous. Again, the volva, in some 

 cases, is not at all cup-like, but clings to the base of the stem like a 

 close sheath, or it may be broken up and appear as patches on the lower 

 end of the stem. 



We see also that on the under side of the cap there are numerous 

 thin, bladelike structures which extend from the stem to the margin 

 of the cap. These are called the gills or lamellae. 



If, now, we should cut a very thin slice from any part of the stem 

 or cap and examine it with a strong magnifying-glass or a microscope, 

 we should find that it is made up of a large number of threadlike 

 hyphae similar to those that compose the mycelium, but that they are 

 crowded so close together that they form a compact body. 



The spores of the mushroom are produced on the sides of the gills. 

 An examination of the surface of one of the gills under sufficient 

 magnification W'Ould show^ us that certain of the hyphae which end 

 there are modified into club-shaped structures, each club having four 

 liny projections at its end. At the end of each of these little pro- 

 jections a spore is borne. The club-shaped structure on which the 

 spores are produced is called a basidium, and all fungi which produce 

 their spores on basidia are called Basidiomycetes. (See Fig. i.) 

 Usually also there are present on the surface of the gills larger and 

 longer club-shaped bodies called cystidia. These project much farther 

 than the basidia and, at least in some kinds of mushrooms, serve to 

 prevent the gills from getting too close together, and thus insure for 

 the spores sufficient room to develop and be liberated. 



SPORE PRODUCTIOX AND LIBERATION 



The spores, as we said, are produced on structures called basidia. 

 These basidia are microscopic in size, so that there is room for a 

 very large number on each gill, and, since each basidium usually pro- 

 duces four spores, the spores are produced in very great numbers. 



