326 A TEXTBOOK OF THEORETICAL BOTANY 



the gills are rather close together we find that special thick cells, called 

 cystidia, are formed on the hymenium which bridge across between the gills 

 and may possibly help to keep the gills sufficiently far apart to allow the 

 spores to fall freely. 



Psalhota Sporophore 



Bandwm 



Bosidiosporei Binucleate Mycelium 



^Uninucleate Mycelium- 



Uninucleate Mycelium 

 Fig. 319. — Life-cycle oi Psalliota campestris. 



Some General Remarks on the Agaricaceae 



In the cultivated mushroom only two basidiospores are produced on each 

 basidiimi. This may be a degeneration as a result of cultivation, or may be 

 the result of a mutation. In most instances the segregation of ( +) and ( -) [ 

 strains takes place in the first division of the basidium, so that ( + ) and ( - ) 

 basidiospores are produced in equal numbers. In certain species of the 

 genus Coprimis the condition is more complex, for segregation appears to take 

 place in the second division, so that four difTerent types of spores are pro- 

 duced. Fruiting bodies are only formed when certain of these spore-types 

 come together (see Volume III). 



The genera of the Agaricaceae are separated mainly on the colour of the 

 spores. In Psalliota they are purple, but white, pink, brown and black 

 spores are found in other genera. Many of the species are edible, but several 

 genera contain poisonous species, notably the genus Amanita, especially 

 Amanita phalloides, the Vernal Toadstool, which is the most deadly (Fig. 

 320). This genus can be recognized easily by the white spores and by the 

 fact that both annulus and volva are present, in contrast to the purple spores 

 and no volva in Psalliota. It is important to remember, however, that the 

 spore colour only develops after the stipe has begun to elongate, and that 

 under certain conditions the volva may become almost completely fused with 

 the base of the stalk. In the genus Coprimis, commonly know^n as the Lawyer's 

 Wig, because of the shaggy exterior of the cap, the gills undergo a curious 



