CHAPTER X 



EXTERNAL CONDITIONS AND SPORE-DISCHARGE— THE EFFECTS 

 OF LIGHT, GRAVITY, HYGROSCOPIC CONDITION OF THE AIR, 

 HEAT, ALTERATION IN THE GASEOUS ENVIRONMENT, AND 

 OF ANAESTHETICS 



Like all other active processes of living organisms, the discharge of 

 spores can only be carried on when external conditions are favour- 

 able. It is now necessary to consider these conditions in detail. 



The Effect of Light. — Whilst in some species, e.g. the Mush- 

 room, the fruit-bodies can undergo perfect development in total 

 darkness, in a number of others the pilei cannot be produced 

 without a morphogenic stimulus given by light. Among the latter 

 are Lentinus lepideus and Polyporus squamosus. When a fruit- 

 body of either of these species is grown entirely in the dark, it 

 develops into a horn-like process without the least trace of a pileus 

 or hymenium (Fig. 16, D, p. 48, and Fig. 20, p. 58). It was found for 

 Polyporus squamosus, however, that, when the development of the 

 pileus has once been initiated in response to the stimulus of light, 

 if the fruit-body is then placed in the dark, further development 

 continues in a normal manner : the usual hymenial tubes are 

 produced and the hymenium gives rise to ordinary basidia which 

 liberate spores in continuous clouds. The production of spores in 

 clouds in the dark, which in one instance lasted for eleven days, 

 proves conclusively that, for Polyporus squamosus at least, the 

 liberation of spores is quite independent of light conditions. For 

 species of Polystictus, Lenzites, Schizophyllum, &c, spore-discharge 

 was found to be quite continuous. The alternation of night and 

 day appeared, as judged by the beam-of-light method, to make no 

 difference whatever to the rate at which spores left the fruit-bodies. 

 It is probably correct to state quite generally for the Hymeno- 

 mycetes that, whilst the morphogenic stimulus of light may or may 



