PSALLIOTA CAMPESTRIS 371 



become purple-brown, dark brown, and nearly black from the 

 large number of spores on their surface." Although it is true 

 that a certain number of waste spores do accumulate on the gills 

 during the period of spore-discharge, yet it is incorrect to attribute 

 the deepening of the colour of the gills chiefly to their presence. 

 The change in colour of the gills is due in the main to the gradual 

 darkening of the cell-sap of all the gill-elements. We have the 

 same phenomenon in such Coprini as Coprinus comatus and C. ster- 

 quilinus. In these species, a pink cell-sap comes into existence 

 shortly before the spores become produced or become pigmented ; 

 and, as the pileus grows older, just prior to the beginning of spore- 

 discharge, the pink sap changes to a very deep brown. In the case 

 of Coprinus sterquilinus, I have been able to prove experimentally 

 that the sap-pigment arises through the action of an oxidising 

 enzyme ; and, doubtless, a similar biochemical cause is responsible 

 for the colour changes in the gills of Psalliota campestris. 



The mottling of the gills, which can be readily made out by 

 anyone who looks for it, was observed by Berkeley, 1 but is not 

 mentioned by Fries, Greville, Stevenson, Massee, or Atkinson. 



Fries 2 described the gills as " saepe liquescentes," Stevenson 3 

 as " often deliquescent," and Massee 4 as " subdeliquescent." The 

 gills, it is true, are very soft ; but, while the spores are being shed, 

 they remain firm and do not undergo deliquescence (autodigestion). 

 In this they differ very markedly from the gills of the Coprini. 

 However, as soon as they have become exhausted by discharging 

 all their spores or have been killed by bruising or other injury, 

 they quickly collapse and become reduced to a pulp, partly perhaps 

 through the action of their own enzymes but chiefly owing to the 

 attack of putrefactive bacteria. On the surface of a dead gill 

 these bacteria multiply with extraordinary rapidity. The only 

 trace of autodigestion in the living gill of a Mushroom is to be found 

 in the collapse of the individual basidia shortly after each has 

 shed its spores, and in the entire disappearance of many of the 



1 M. J. Berkeley, The English Flora, vol. v, Part II, Fungi, 1836, p. 107 ; 

 also cited in Massee's British Fungus-Flora, London, vol. i, 1892, p. 411. 



2 E. Fries, Monographia Hymenomycetum Sueciae, Upsaliae, vol. i, 1857, p. 406. 



3 J. Stevenson, Hymenomycetes Britannici, London, vol. i, 1886, p. 306. 



4 G. Massee, British Fungus-Flora, London, vol. i, 1892, p. 411. 



