HELIOTROPISM OF ASCI IN DISCOMYCETES 317 



through an angle of about 45°. Doubtless the curvature of these 

 asci was heliotropic in origin. 



Since, in a fruit-body of a Morchella. the asci in each alveolus 





Fig. 157. — Morchelhi conica. A, a thin meJiaii-vertical section tlirough 

 a receptacle (fruit-body) : a, the stipe ; b, the pileus ; c, a longi- 

 tudinally elongated alveolus (pit) seimrated from neighbouring alveoli 

 by dissepiments d d and having transverse ridges e within. The 

 hymenium / covers the interior surface of each alveolus and is 

 absent only on the free edges of the dissepiments, which form sterile 

 ribs g g. The broken line indicates the outermost limits of the alveoli. 

 B, two alveoli of A, shown on a larger scale : a, the pileus-flesh ; b b, 

 dissepiments ; c c, transverse ridges ; d, the hymenium covering the 

 interior of the alveoli, but absent from the exterior edges (ribs) of 

 the dissepiments ; e, a portion of the hymenium illustrated on a 

 larger scale in Fig. 158. The asci are all directed toward the source 

 of strongest light and therefore toward the mouth of each alveolus. 

 The arrows indicate the general directions in which the spores are 

 shot, and the clouds of spores outside the mouths of the alveoli have 

 just been formed in consequence of the receptacle having suddenly 

 puffed in response to the application of heat from a lamp (c/. Fig. 128). 

 A, natural size. B, four times the natural size. 



point toward the mouth of the alveolus and since the operculum of 

 each ascus is situated symmetrically at the end of the ascus, it is 



