1 66 



RESEARCHES ON FUNGI 



the spores, one might obtain a direct test. It was also thought 

 that an actual determination of the rate of fall of spores would 

 throw light upon the distribution of bacteria, spores, and other 

 organic particles in air, and also help to explain fruit-body structure. 

 A considerable amount of preliminary experimentation was 

 undertaken, during which observations were made upon the rates 

 of fall of spores of various shapes and sizes in still air. The spores 

 of Amanitopsis vagina ta were then chosen as material for a critical 

 test of Stokes' Law for the following reasons : (1) They are spherical 

 except for a tiny " tail," and smooth-coated (Fig. 55, A, B, and C, 

 p. 162). (2) They are comparatively large, so that one can measure 

 their diameters, which are about 10 n wide, very 

 accurately with the Poynting Plate Micrometer. 

 (3) Their density is almost that of water, and 

 can be measured within 1 per cent, of ac- 

 curacy. 1 (4) They could easily be procured, for 

 the fruit-bodies of Amanitopsis vaginata came 

 up in sufficient abundance in Sutton Park, 

 which was not many miles from the laboratory. 

 Fresh fruit-bodies (Plate IV., Fig. 30) could be 

 obtained throughout August and September, 

 during which time the critical experiments were 

 made. The relations of the spores to the fruit- 

 body are shown in Fig. 56. 

 An experiment to measure the rate of fall of Amanitopsis spores 

 was carried out in the following manner. A fresh fruit-body was 

 obtained from the woods and used within a few hours of being- 

 gathered. Due care was taken in carrying the fruit-bodies to the 

 laboratory, upon reaching which they were immediately placed 

 upright in a wet sand-bath and covered over with a large bell-jar. 



A small piece of the pileus, including portions of three gills, was 

 then dissected out (Fig. 57) and placed in a compressor cell in the 

 position shown in Fig. 58, p. To prevent the falling spores from 

 drying, two soaked pieces of blotting-paper or cotton-wool, b, and a few 

 drops of water, w, were then added. Upon the cap being adjusted, the 

 piece of fungus became fixed by slight compression and hermetically 

 1 Vide Chap. XIII. 



Fig. 57. — Diagram to 

 show the shape of a 

 section from a pileus 

 placed in the com- 

 pressor cell. The gills 

 are directed vertically 

 downwards. 



