^n 



h cT. 



1 66 



HP:sEAIU HKS ox FUNGI 



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

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

 throAv 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 Avhich observations Avere made upon the rates 

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

 of Amanitopsis vaginata were then chosen as material for a critical 

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

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

 p. 1G2). (2) They are comparatively large, so that one can measure 



their diameters, which are about 10 fi wide, very 

 accurately with the Poynting Plate Micrometer. 

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

 can be measured within 1 per cent, of ac- 

 curacy.^ (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. 

 -Diagram to Fresh fruit-bodics (Plate IV., Fig. 30) could be 

 iSon^a^ViL: Obtained throughout August and September, 

 placed in the com- during which time the critical experiments were 



pressor cell. The gills , ^ . 



are directed vertically made. Tho relations of the spores to the fruit- 

 downwards. 11 1 . -r-i- _,. 



body are shown m rig. ;)0. 



An experiment to measure the rate of fall of Amanito})sis 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 Avhich they were immediately })laced 

 upright in a Avet sand-bath and covered over Avith a large bell-jar. 



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

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

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

 drying, tAvo soaked pieces of blotting-paper or cotton-Avool, h, and a few 

 drops of Avater, w, Avere then added. Upon the cap being adjusted, the 

 piece of fungus became fixed by slight compression and hermetically 



1 riW(;Chap. XTIT. 



Fig. 



i>t.- 



