466 RESEARCHES ON FUNGI 



owing to the relative smallness of its basidia and paraphyses and the 

 consequent denser packing of these elements. 



The spore-discharge period of a wild Psalliota campestris was observed 

 to be of 4-6 days' duration. Spores begin to be discharged from a 

 fruit-body when the gills are pink and the pileus is still expanding, and 

 they continue to be discharged even when the top of the pileus has 

 become quite flat and the gills have turned dark chocolate-brown. The 

 number of spores produced by a large Mushroom was calculated to be 

 upwards of 10,000,000,000. 



In Psalliota campestris, just as in Panaeolus campanulatus, irregular 

 waves of hymenial development constantly pass over the surface of 

 each gill, thus changing the pattern of the mottling ; and the elements 

 of the hymenium can all be referred to one or other of the following 

 five classes : (1) past-generations basidia, (2) present-generation basidia, 

 (3) coming-generation basidia, (4) future-generations basidia, and (5) 

 paraphyses. 



In Psalliota campestris, as in Panaeolus campanulatus, the paraphyses 

 are destined to be sterile from the first. They become vacuolated 

 early and swell up considerably during the gradual exhaustion and 

 collapse of the basidia. At the end of the spore-discharge period, all 

 the basidia are collapsed and dead, but all the paraphyses are living. 



The basidia of wild forms of Psalliota campestris are usually tetra- 

 sterigmatic and quadrisporous, whilst the basidia of cultivated forms 

 are usually disterigmatic and bisporous. 



In the hymenium of cultivated forms of Psalliota campestris a certain 

 proportion of the basidia are usually monosterigmatic and unisporous. 

 The unisporous basidia are equal in size to the bisporous ; but the spore 

 of a unisporous basidium has about twice the volume of one of the 

 spores of a bisporous basidium. A cultivated Mushroom therefore has 

 spores of two sizes, large and small. 



The development of the four spores on a basidium of a wild Mush- 

 room, from their first appearance as tiny rudiments to their discharge, 

 was observed to occupy about 7-5 hours. A single spore (1) takes 

 30-40 minutes to grow from a tiny rudiment to full size, (2) remains 

 colourless for the next two hours, (3) gradually becomes pigmented 

 during the next two hours, (4) remains in the fully pigmented condition 

 on the end of its sterigma for a further 3 hours and about 10 minutes, 

 and (5) is then discharged. The discharge of a Mushroom spore takes 

 place with drop-excretion as in other Hymenomycetes. 



In Psalliota campestris there is no plane sharply dividing the sub- 

 hymenium from the hymenium ; but the subhymenium passes gradually 

 into the hymenium, owing to the fact that the basidia are attached to 

 subhymenial cells at different depths. 



Secotium agaricoides resembles a Puff-ball in general appearance, 

 but is nevertheless closely allied to Psalliota. 



