EXTERNAL CONDITIONS AND SPORE-DISCHARGE 127 



pile in March at about — 17° C. after being exposed for several months 

 to severe frost. When brought into the laboratory they soon began 

 to shed their spores, and within a few hours produced well-marked 

 spore-deposits. 1 On the other hand, extreme heat probably causes 

 a heat rigor, for when some fruit-bodies of Lenzites betulina were 

 exposed to a temperature of 39° C. for half-an-hour and then cooled 

 to an ordinary room temperature, two hours passed by before the 

 fall of spores was resumed. 



The range of temperature which permits of spore-discharge — for 

 Lerr.it es betulina about 0° to 0O C. — probably coincides with the 

 range of temperature permitting the growth and development of the 

 spores. As soon as the spores are ripe they are probably shot off. 

 If one watches the discharge of spores from the basidia with the 

 microscope, one finds that spores which look ripe, i.e. which have 

 attained their full size and proper colour, do not long remain on 

 their sterigmata. The rate of spore-discharge seems, therefore, to be 

 an indication of the rate of spore development. 



So far, opportunity has not been found for determining the range 

 of temperature within the limits of which the liberation of spores is 

 possible for succulent, non-xerophytic, ground Agarics which flourish 

 during summer. It seems to me probable, however, that for many 

 species, e.g. the Mushroom, the minimum temperature for shedding 

 spores is several degrees above the freezing point of water. To what 

 extent frost is fatal to the reproductive organs of Hymenomycetes 

 still requires investigation. 



The Effect of Alteration in the Gaseous Environment. — The 

 pileus of a small fruit-body of Marasmius oreades, about 1 inch in 

 diameter, was divided into three portions. One of them was placed 

 in a suitable glass vessel of about 0'75 litres capacity, through 

 which a strong stream of hydrogen was made to flow for ten minutes. 

 The stop-cocks were then closed. By similar means the second 

 portion of the pileus was surrounded by an atmosphere of carbon 



1 Possibly the fruit-bodies began to shed their spores immediately they had 

 been unthawed and raised to the temperature of the laboratory. Unfortunately, 

 when these experiments were made, I had not developed the beam-of-light 

 method, and the formation of a macroscopic spore-deposit was relied upon as a 

 test for the liberation of spores. 



