1 88 HKSEAIH'TTES ON FUNGI 



within 1 per cent, of the totiil horizontal distance to which it is 

 projected. An important conclusion which may be drawn from this 

 calculation is that it would be extremely ditlicult, if not impossible, 

 to observe the horizontal flight of the spores. The horizontal move- 

 ment is completed in ^ ij^^ second. It is very questionable if the 

 human eye could observe such a movement of a dark body at all, 

 and particularly under the conditions of observation necessitated by 

 the size of the spores, the position of the basidia, and the uncertainty 

 of the time of spore-discharge. These theoretical considerations fall 

 in line with my observations, for I have never yet succeeded in 

 watching the horizontal flight of a spore from its sterigma. 



The results of the investigations upon the motion of a spore of 

 Amanitopsis vaginata, 10 /x in diameter, when projected from its 

 sterigma in a horizontal direction, may be summed up as follows : — 



By observation — 



Maximum horizontal distance of projection = 0'02 cm. 

 Terminal velocity of fall = 0"5 cm. per second. 



By calculation — 



The terminal velocity of fall is reached after a distance of 9 /x (which is 



less than the diameter of a spore) has been traversed. 

 The terminal velocity of fall is reached in ^^jy second approximately. 

 The spore arrives within 1 per cent, of its total horizontal flight {i.e. it 



goes 0*0198 cm.) in jjjj second. 

 The initial horizontal velocity is 40 cm. per second. 



When one compares the movement of a spore with that of a 

 pebble projected in like manner, the differences at first appear to be 

 remarkable. However, it nmst be remembered that a spore has an 

 enormous surface in proportion to its mass as compared with a 

 pebble. The air, therefore, in proportion to their masses, ofters a 

 vastly greater resistance to the movement of a spore than to that of 

 a pebble. 



in Plate I., Fig. 4, the paths of spores between the gills of a 

 Mushroom are shown, whilst in the text-figures 56 (p. 165) and 66 

 similar illustrations are given for Amanitopsis vaginata and Poly- 

 poriis squamosum respectively. It is evident that the spores are 

 shot outwards from the hymenium in such a manner that they are 

 projected clear of the hymenium and yet not i'ai- enough to strike 

 the opposite gill. The air is a delicate regulator in this matter. 



