THE COPRIXUS TYPE OF FRUIT-BODY 205 



metre behind it. The five zones described, retain the same 

 relations to one another during the whole two days or so required 

 for the complete discharge of the spores. They move upwards 

 simultaneously from the bottom to the top of each gill (Plate II., 

 Figs. 8, 9, and 10). The zone of spore-free basidia, and the adjacent 

 portions of the zones of spore-discharge and autodigestion, can 

 often just be distinguished with the naked eye upon a gill, for 

 together they give the appearance of a very thin whitish line 

 next to the thin black liquid film on the gill edge and separating 

 this from the general gill surface which, owing to the vast number 

 of spores borne by the mature basidia, is uniformly black. 



It is evident that autodigestion plays a very important part 

 in spore-discharge. Its function is wholly mechanical. It destroys 

 the spore-freed portions of the gills and so clears them out of the 

 way. Only by the removal of these obstacles could the pileus 

 gradually turn outwards and thus cause the production of spaces 

 between the lower ends of the gills higher and higher up as these 

 become shorter and shorter. Such spaces are absolutely necessary 

 to permit of the liberation of the spores from the zones of spore- 

 discharge. The basidia shoot out their spores horizontally into 

 the spaces between the gills (Plate III., Figs. IG and 17). The 

 maximum horizontal distance to which the spores travel, before 

 their horizontal motion is reduced to zero by the resistance of 

 the air, is about 0-1 mm. After making the usual sporabolic 

 curves, the spores fall vertically downwards with a steady terminal 

 velocity of about 4 mm. per second.^ Since the zones of spore- 

 discharge are so near the gill edges, the spores have only to fall 

 a distance of about 5 mm. between two gills in order to effect 

 their escape. The risk of the spores striking the gill sides is 

 thereby reduced to a minimum. As the spores fall below the 

 pileus, doubtless they lose water rapidly.- Their velocity pro- 

 bably diminishes to about 2 mm. per second in the course of a 

 minute. On leaving the fruit-body, the spores are carried off 

 by air-currents which scatter them far and wide. The discharge 

 of spores into the air takes place day and night continuously. It 

 has already been mentioned that a large fruit-body was found to 

 1 Chap. XV. 2 Qhap. XVI. 



