262 RESEARCHES ON FUNGI 



which are shot away. I have not investigated the recoil in S. pro- 

 tracta, but Dr. E. C. Stakman has informed me that he has observed 

 the recoil in the thin-stalked apothecia of Sderotinia sderotiorum : 

 as puffing took place, the cups containing the asci were visibly- 

 pressed backwards. Such a recoil gives an indication of the energy 

 with which the projectiles discharged from the asci bombard the air 

 and set it in motion . 



The Blast of Air and the Dispersal of the Spores. — If the asci of 

 a Sarcoscypha protracta fruit-body were to explode one after the 

 other as they ripen, it is probable that the eight spores of each ascus 

 would not be shot up into the air for more than 3-4 cm., and no 

 appreciable blast of air could come into existence to raise them still 

 further. On the other hand, when a hundred thousand asci explode 

 together, i.e. when puffing takes place, the bombardment of the air 

 by the spores and ascus-drops collectively is sufficient, as we have 

 seen, to create a blast of air which can carry the spores with it for 

 several inches after they have lost the velocity given to them by 

 the ascus-guns. Consider now a fruit-body under natural conditions 

 in a Poplar wood. Its stipe is negatively geotropic and its apothe- 

 cium therefore looks upwards to the sky. If the asci were all to be 

 discharged in succession as they ripen, none of the spores (we may 

 suppose) would travel upwards more than an inch or two ; but, 

 if the asci ripen one by one and then wait before exploding until 

 some suitable stimulus sets them all off together, then the spores 

 may be carried upwards by the blast of air. which they bring into 

 existence, to a height of 5-7 inches. After being carried upwards 

 into the air, the spores are borne away more or less horizontally by 

 the wind and are thus dispersed. The nearer to the ground, the less 

 wind there is ; and every extra inch the spores can be raised into the 

 air by discharge from the apothecium, the stronger mil be the wind 

 which they will encounter and the greater the chance that they will 

 be dispersed widely and find suitable conditions for propagating the 

 species. Once more we are provided with an instance where union 

 is strength and where collective action is better than individual 

 action. 



Concluding Remarks. — Oiu- knowledge of the phenomenon of 

 spore-discharge in the Discomycetes is still very incomplete. With 



