THE BEAM-OF-LIGHT METHOD 



97 



The spores of white-spored species stand out in the beam of light 

 as distinct white particles, whilst the purple-brown ones of the 



FlG. 37. — Diagram illustrating the discharge of spores from a 

 fruit-body of Polystictus versicolor as seen by the beam-of- 

 light method. The fruit-body is pinned in its natural 

 position to a piece of cork attached to a circular glass 

 cover placed upon a beaker. A stream of spores is carried 

 round within the beaker very slowly by convection cur- 

 rents and gradually breaks up so that the spores become 

 scattered fairly uniformly. Reduced to about §> 



Mushroom and the black ones of Coprini present brownish and dull 

 metallic appearances respectively. 



It has been determined, by methods to be explained subsequently, 

 that very small spores, such as those of Collybia dryopJiila, in still 

 air fall at the rate of about 0*5 mm. per second, and that the very 

 largest, such as those of Coprinus plicatilis, fall at the rate of about 



