1042 



MUSHROOM 



MUSHROOM 



French word "mousseron," and is sometimes pronounced 

 "mushroons," or "musheroons" by English-speaking 

 people in America. Mushroom and toadstool are some- 

 times used as synonymous terms, especially in speak- 

 ing of the group as a' whole. It is difficult, therefore, to 

 give either a satisfactory definition of the word Mush- 

 room, or satisfactorily to limit the range of forms for 

 which the name may be used. In a horticultural sense 



1440. The gardener's Mushroom, Agaricus campestris (X 



it is applied to Agaricus campestris (Fig. 1440) in cul- 

 tivation, and since that is the plant with which we are 

 first interested here, we may proceed at once to a de- 

 scription of its form, structure, development, etc., and 

 follow with briefer descriptions and comparisons of a 

 few of the many species belonging to this large group. 

 Form and Structure of Agaricus campestris. The 

 form of the common Mushroom is more or less um- 

 brella-shaped, and is well represented in Fig. 1441. 

 The prominent parts of the plant are the stem, with its 

 ring (a); and the cap,with the gills on the under side. The 

 cap, or pileus, as it is technically called, is the upper 

 expanded part, and varies from 2 to 4 or 5 indies in 

 diameter. It is usually white in color, but forms occur 

 both in the field and in cultivation in which the upper 

 surface is more or less brownish, especially as the plants 

 become old. The surface is usually smooth, though it 

 often presents a silky texture from the numerous mi- 

 nute fungous threads or mycelium, the structural ele- 

 ment of the entire plant. While the surface is smooth 

 in a majority of specimens, many forms are more or 

 less scaly, due to the fracture of the surface and sepa- 

 ration of the numerous small areas, especially in the 

 specimens with brownish caps. The "flesh" or "meat" 

 of the cap is white. The stem, or stipe, is usually cyl- 

 indrical, 1-3 in. long by %-% in. in diameter, whitish 

 in color, and nearly or quite solid. The "ring," or annu- 

 lus, forms a collar joined around the stem near the top. 

 It is very delicate, easily rubbed off, and sometimes 

 not present because the veil from which it is formed is 

 torn in fragments as the cap opens out. The gills, or 

 lamellae, on the under side of the cap are of great im- 

 portance in showing relationship, and also probably in 

 reproduction in the case of plants propagated under 

 natural conditions, since they form the fruiting surface 

 of the Mushroom. The gills are in the form of narrow, 

 thin plates, shaped somewhat like a knife-blade, at- 

 tached by one edge to the under side of the cap and 

 radiating from a point near the stem out to the margin 

 of the cap. The longest gills extend for this distance 

 and mark off triangular areas which are filled with suc- 

 cessively shorter gills, all reaching the margin of the 

 cap, so that the entire under surface of the cap is well 

 covered with them. The surface of the gills is the 

 fruiting surface of the plant, and this economy in the 

 arrangement of the gills provides for a very large fruit- 

 ing area. The color of the gills when the plant is very 

 young is white. They soon, however, become pink in 



color, and as the plant ages become purple-brown or 

 blackish in color, due to the immense number of spores 

 borne on the surface. One can gain a good idea of the 

 number of spores borne on a single plant by cutting a 

 cap from a Mushroom, just at maturity, and placing it, 

 gills downward, on a piece of white paper for a few 

 hours. The spores fall from the gills and pile up in 

 ridges, giving an exact print of the spaces between the 

 gills. 



The parts of the plants enumerated above 

 are easily seen. Other important structural 

 characters are seen with the aid of the mi- 

 croscope. A thin section across the gills 

 when seen with the microscope shows the 

 structure as seen in Fig. 1442. The middle 

 part of the gill is the trama. On either side 

 of the trama is the subhymenium, composed 

 of branches from the trama and forming 

 short cells. The cells of the subhymenium in 

 turn give rise to the basidia (basidium), club-' 

 shaped bodies, which form a palisade layer of 

 cells over the entire surface of the gill. This 

 palisade layer of the basidia forms the fruit- 

 ing surface, or hymenium. 



At the end of each basidium are either 2 

 or 4 slender, pointed processes, the sterig- 

 mata (sing, sterigma). These bear each a sin- 

 gle spore, the basidiospore. The usual num- 

 ber of sterigmata on the basidium in the 

 Agaricini is 4; but in Agaricus campestris 

 the number seems to vary from 2 to 4. In 

 plants grown in a Mushroom house, 2 have 

 been found, while plants from the field show 4. 

 Whether the number 2 for cultivated forms 

 is constant, or 4 for the field forms, has not 

 been determined. 



Development of Agaricus campestris. The spores of 

 the Mushroom in the field probably of ten germinate and 

 produce new mycelium or "spawn," though this is not 

 necessary for the continuance of the plant from one year 

 to another, since the spawn can live through the winter 

 in the soil, and the following year then spreads. In 

 ordinary Mushroom culture, however, the spores prob- 

 ably play little part in the propagation of the plant, since 

 this is accomplished by the growth and propagation of 

 spawn. If the soil where plants are growing is carefully 

 dug away there will be seen slender and irregular whit- 

 ish cords coursing through it, and some of them attached 

 to the base of the stem. These whitish cords are what 

 the horticulturist calls "spawn." They are cords of my- 

 celium, and are composed of numerous very slender and 

 "delicate whitish threads. This is the vegetative portion 

 of the Mushroom. If the soil at the base of a tuft of 



1441. Cultivated Mushroom, Agaricus campestris. 



young plants in a Mushroom bed be washed away, a 

 large number of these cords will be exposed. This is 

 the part of the plant which grows and spreads through 

 the soil, absorbing solutions of the organic matter in the 

 soil for food. 



Button Stage. After an abundance of the mycelium, 

 or spawn, is formed there appear here and there on the 



