CHAPTER II 



PSATHYRELLA DISSEMINATA 



Relations of Lepiofa cepaestipes and Psathyrella disseminala — Psathyrella dif<- 

 seminata. Its Relation uith Tree Stumps — The Structure and Functions of 

 an Ozonium — Description of the Fruit-body — The Spore-discharge Period — 

 The Gills — The Hymenium — Pilocystidia, Pleurocystidia, Oheilocystidia, and 

 Caulocystidia — Correlation of Facts — Remarks on Taxonomy 



Relations of Lepiota cepaestipes and Psathyrella disseminata. — 



Psathyrella disseminata is one of the two fuugi upon which the 

 Psathyrella Sub-type of fruit-body organisation is based. The other 

 fungus, Lepiota cepaestipes, has just been described in detail. Both 

 species are ephemeral, and both have a similar arrangement of tlic 

 hymenium ; and, so far as the production and liberation of spores 

 is concerned, they function in the same manner. However, the 

 resemblance which they show in some of their structural and physio- 

 logical characters does not prove that they are genetically closely 

 related, for they differ greatly in a number of ways. Thus (1) the 

 gills of the Psathyrella split from above downwards like those of 

 many Coprini, whereas in the Lepiota the gills remain intact ; 

 (2) the arrangement of the tramal cells in the gills of the Psathy- 

 rella is entirely different from that of the Lepiota ; (3) the spores 

 of the Lepiota are colourless, whereas those of the Psathyrella are 

 black ; (4) the stipe of the Lepiota is encircled by a well-developed 

 annulus, whereas the stipe of the Psathyrella is perfectly bare ; and 

 (5) the gills of the Lepiota are quite free from stipe, whereas those 

 of the Psathyrella are adnate. It seems to me, therefore, that the 

 two species have arrived at their similar arrangements for the rapid 

 production and liberation of spores by convergence and not by direct 

 descent from a common ancestor. Because two fungi show similar 

 arrangements for the production and liberation of spores, that, in 



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