240 RESEARCHES ON FUNGI 



in contact with dry air ; but it seems certain that it can be given by 

 chemical means, as when an ascus is caused to explode when treated 

 with silver nitrate, mercuric chloride, alcohol, and certain other 

 poisonous substances. Where there is a gradual emptying of ripe 

 asci, as, according to De Bary, occurs in Bulgaria, Exoascus, &c., 

 probably the activity of the guardian protoplasm is controlled by 

 stimuli arising from internal developmental changes taking place in 

 the ascus as a whole. 



At present there does not seem to be any evidence that puffing 

 takes place under natural conditions, and it would therefore be 

 fruitless to discuss whether or not the phenomenon has any useful 

 biological significance. It may be added that puffing, when observed 

 in still air with the aid of a beam of light, is a beautiful exhibition 

 of sporocarp activity. It may be likened to the grand finale of 

 sky-rockets in a pyrotechnic display. 



The Physics of the Ascus Jet in Peziza. From my obser- 

 vations upon the discharge of individual asci, it is clear that 

 the spores contained within an ascus jet become separated from 

 one another within a fraction of a second, between the time that 

 they leave the ascus mouth and the time that they suddenly 

 appear as eight separated particles in the beam of light. We 

 shall now inquire into the nature of the forces which serve 

 to detach the spores from one another during their ascent into 

 the air. 



The ascus wall contracts during the ejection of the ascus jet, 

 so that the ascus volume becomes reduced to about one-half 

 (Fig. 79, E and F). The nature of the contraction affords a 

 strong argument for the belief that the pressure exerted upon 

 the ascus contents is greatest at the beginning of the discharge, 

 and that it diminishes continuously and rapidly during the dis- 

 charge, so that it finally becomes zero when the discharge has been 

 completed. The ascus jet on leaving the ascus mouth may be 

 regarded as a more or less cylindrical column of fluid containing 

 eight spores situated in a row. Owing to the nature of the ascus 

 contraction, it seems almost certain that the front end of the 

 ascus jet must be shot outwards with the greatest velocity and 

 the rear end with the least. The whole jet after its emission 



