394 RESEARCHES ON FUNGI 



The existence of a gill-chamber causes the gills, during their de- 

 velopment, to be subjected to more even conditions of temperature 

 and moisture than would be possible in its absence. The chamber 

 floor also bars out from access to the gills the most nutritious 

 and vulnerable parts of the whole fruit-body such small marauding 

 animals as Fungus Gnats (Mycetophilidae), Springtails (Collembola), 

 and Mites (Arachnida) ; and it also keeps away Bacteria and the 

 spores of parasitic Fungi. The development of a gill-chamber 

 which persists until spore-discharge is about to begin, i.e. until the 

 last possible moment when it can be of service, is a beautiful con- 

 trivance which was probably added in a late stage of the evolution 

 of the Mushroom. The annulus, owing to its delicacy, shrivels up 

 soon after its definite formation and so comes to offer but a very 

 slight obstacle to the removal of the falling spores by the wind. 



Conditions for the Origin of Fruit-bodies. The conditions under 

 which the fruit-bodies of Psalliota campestris come into existence 

 in the first place are not as yet by any means fully understood. 

 We know that the mycelium vegetates in the substratum of turf 

 or rotted horse manure for some weeks or months and that it then 

 rapidly produces mushrooms. The mushrooms never arise at any 

 depth in the substratum, but always at its surface. Two questions 

 in this connection await an answer : (1) what internal changes 

 cause the mycelium to proceed from the vegetative to the repro- 

 ductive stage, and (2) what external stimulus decides that the 

 fruit-bodies, when formed, shall arise at the surface of the sub- 

 stratum and nowhere else ? In the absence of exact knowledge 

 our answers to these questions can only be speculative. 



The recent investigations of Mile Bensaude, Hans Kniep, and 

 Miss Mounce have proved conclusively that in the Hymenomycetes, 

 as in the Phycomycetes, some species are homothallic and others 

 heterothallic. 1 In a homothallic species, e.g. Coprinus sterquilinus, 

 fruit-bodies are produced rapidly and perfectly upon a mycelium 

 of monosporous origin. On the other hand, in a heterothallic 

 species, e.g. Coprinus fimetarius, Schizophyllum commune, and 

 Coprinus lagopu-s, this is usually not the case. Thus, according 



1 For a detailed treatment of the problem of sex in Hymenomycetes vide infra, 

 vol. iv, Chapters on Sex. 



