400 RESEARCHES ON FUNGI 



summer were to begin their development only after the soil had 

 become watered, probably they would not appear in the pastures 

 under the most favourable circumstances for at least ten days. 

 The early stages of fruit-body development take place very slowly 

 and cannot be hurried beyond a certain pace. The growth of a 

 fruit-body in size undergoes acceleration from day to day, and 

 the last stage, in which the stipe elongates and the pileus expands, 

 is passed through so rapidly that many people are apt to think that 

 a mushroom completes its full development in a single night. The 

 rapidity of the expansion of a mushroom in its final phase of growth 

 has been proverbial from the most ancient times and is, of course, 

 based on the observations of the mushroom-gatherer bent on 

 booty for the table ; but it must not be forgotten that this marvel 

 of nature is only the climax of many days of slow and steady, 

 although usually invisible, developmental progress. 



The Spore-discharge Period and the Number of Spores. The 

 length of time occupied by any fruit-body in the discharge of spores 

 may be conveniently called the spore-discharge period. 1 In order 

 to determine this period for Psalliota campestris recourse was had 

 to the following procedure. Two clods of turf each bearing a single 

 mushroom, which was just bursting its gill-chamber and under- 

 going rapid expansion, were dug up in a field with great care so 

 as not to injure the fungi in any way, and were removed to a potting- 

 shed. Here each clod, which was about 5 inches in diameter 

 and 5 inches deep, was inserted in an 8-inch pot and packed 

 below and at the sides with wet soil, so that each mushroom took 

 up a vertical position similar to that which it had had in nature. 

 Each pot was then covered by a similar but inverted pot, and the 

 hole at the top was partially closed with a plug of cotton- wool. 

 The two preparations were then removed to a somewhat cool room 

 in a house which was temporarily used as a laboratory. There- 

 upon, at 10.15 A.M., some glass slides were placed beneath each 

 mushroom. One of the mushrooms was a little further advanced 

 in development than the other. Let us call the more advanced 



1 A large Horse Mushroom (Psalliota arvensis) shedding spores in a field during 

 the spore-discharge period is shown semi-diagranimatically in Fig. 76, vol. i, 1909, 

 p. 218. 



