PUFFING IN THE DISCOMYCETES 257 



apex and that the ascostoma subsequently takes up its oblique position 

 owing to a response of the ascus end to a heliotropic stimulus. Thus 

 the oblique position of an ascostoma at the end of any ascus is regarded 

 by me not as a purely " morphological character " depending for 

 its origin on internal growth stimuli only, but as a physiological 

 character depending on an external stimulus, namely, that of light. 

 Experimental Proof that a Fruit-body, when it puffs, produces 

 a Blast of Air. — When a fruit-body of Sarcoscypha jyrotrada is held 

 horizontally in the still air of the laboratory and it puffs, the cloud 

 of spores set free travels horizontally to a distance varying from 

 about 8 to 17 cm. (7 inches), according to the intensity of the puff. 

 The greater the number of spores set free at one time, the louder is 

 the hiss made by them as they pass through the air and the farther 

 do they travel before becoming dispersed irregularly. As I watched 

 the puffing of a number of fruit-bodies tested one by one in the 

 laboratory, it seemed that the spore-cJoud — at any rate in the latter 

 part of its journey — w^as being borne along as if by a blast of air. 

 I therefore decided to test this idea by means of experiment. On 

 May 9, 1925, I went to the Poplar wood where Sarcoscypha protracta 

 grew and gathered a considerable number of fruit-bodies. As the 

 temperature of the air in the wood w^as only a few degrees above the 

 freezing point of water, the fruit-bodies would not puff ; but, after 

 being brought into the laboratory and left in closed Petri dishes at 

 a temperature of about 70° F. for about an hour, many of them puffed 

 freely when they were removed from their Petri dishes and were 

 held in the fingers in the relatively dry air of the laboratory. 



The apparatus employed for demonstrating that a fruit- body of 

 Sarcoscypha protracta, when it puffs, produces a blast of air is shown 

 in Fig. 124. What is represented was spread out in a horizontal 

 plane, and the observer is supposed to be looking down on it from 

 above. A test-tube a with an open side-pipe b (shown in section at c) 

 is held in a horizontal plane by the clamp e which is attached by 

 the clamp d to the vertical rod of an iron stand. The position of a 

 card- board screen is shown at / and g. The apparatus was set up 

 on a laboratory table near a window, so that strong daylight fell 

 upon it. In front of the mouth of the side-pipe 6, as shown around i. 

 there was a black back-ground. 



VOL. VI. 



