EXTERNAL CONDITIONS AND SPORE-DISCHARGE 123 



the chamber was saturated with moisture. When crystals of 

 calcium chloride were placed in the cell, the spores continued 

 to fall for some time, until the piece of pileus had shrunk 

 appreciably and was evidently drying up. 



It can easily be observed with the beam-of-light method that, 

 if a fruit -body of Polystictus versicolor, Lenzites betulina, &c., 

 is allowed to dry up slowly, when a certain amount of water has 

 been lost, the rate of spore-discharge becomes slower and slower. 

 As desiccation proceeds spore-fall ceases altogether. Insufficient 

 access to water must often, in nature as in the laboratory, 

 especially in the case of the xerophytic fruit-bodies growing on 

 logs ,and sticks, lessen the rate of spore-discharge and lead to a 

 corresponding increase in 'the length of the spore-fall period. 



The general conclusion, to which numerous observations of 

 the kind just described have led me, is that, so long as a fruit- 

 body has sufficient moisture in itself, the dryness or dampness 

 of the atmosphere without makes no appreciable difference to 

 the rate of spore-discharge. 



The Effect of Heat. The liberation of spores, like all other 

 vital processes, can only be carried on within certain limits of 

 temperature. Doubtless each species has its own particular 

 minimum, optimum, and maximum for this function. 



In all the species so far investigated, the discharge of spores 

 takes place rapidly at ordinary room temperatures. It slackens, 

 however, when the temperature is sufficiently lowered ; but in 

 several instances it was found to continue even at the freezing 

 point of water, although with much diminished vigour. A slowing 

 down of the rate of spore-discharge also occurs when the tem- 

 perature is gradually raised above the normal; and when a 

 certain temperature has been reached, the hymenium becomes 

 altogether inactive. The maximum temperature for the discharge 

 of spores, however, is appreciably lower than the maximum for 

 vitality. 



For the purpose of determining whether spore-fall still continues 

 at freezing point, a cold- room was made use of. The room had 

 two doors, one opening out-of-doors and the other into a passage 

 within the University building. The temperature of the room 



