256 RESEARCHES ON FUNGI 



Vj = 50 cm. per second. Since V is only 0*5 cm. per second, the 

 conclusion may be drawn that the ascospore group falls about one 

 hundred times more rapidly than the basidiospore. Since for 

 high velocities Stokes' Law breaks down and the resistance of 

 the air becomes proportional to a higher power of the velocity, 

 the rate of fall of the ascospore group is in reality somewhat 

 less than 50 cm. per second. Its actual value, however, must 

 still be enormous compared with that for the velocity of fall of a 

 basidiospore. The latter was observed to be only about 0-5 cm. 

 per second. 



Since the terminal vertical velocity of an ascospore group of the 

 Ascobolus has been calculated to be of the order of 50 cm. per 

 second, we can easily understand why it is that a thick spore-deposit 

 often collects within a short radius of the fruit-bodies. Ordinary 

 convection currents, such as occur in dwelling-rooms, or slight 

 movements of the air in the open, can be of little use in scattering 

 the ejected ascus contents, although dispersion may be effected by 

 winds of moderate strength. On the other hand, basidiospores, 

 owing to their tiny size, fall very much more slowly than the 

 ascospore groups, and in consequence are splendidly adapted for 

 transport through the air. Even very slight convection currents, 

 such as occur almost universally near the earth's surface, are able 

 to carry them about and render the position where they come to 

 settle a matter of the greatest uncertainty. 



The fruit-bodies of Ascobolus immersvus exhibit a number of 

 special adaptations to a coprophilous mode of existence which 

 enable them to liberate their spores from the sides of horse-dung 

 balls, &c., with success. These adaptations may be summarised as 

 follows : (1) The protrusion of the ripe asci, just before discharge, 

 to some distance beyond the surface of the hymenium; (2) the 

 diurnal periodicity in the ripening and discharge of successive series 

 of asci ; (3) the heliotropic reaction of the asci whilst becoming 

 protuberant; and (4) the great violence of spore-discharge. The 

 protrusion of the ripe asci far beyond the hymenial surface permits 

 of the asci making positive heliotropic curvatures. Such reactions 

 to light would be impossible if the asci were entirely embedded 

 in the hymenium like those of Pezizae. The periodicity in the 



