HELIOTROPISM OF ASCI IN DISCOMYCETES 283 



Several fruit-bodies of Ciliaria scutellata which were expanded 

 horizontally on the top of boards in one of the ice-houses were 

 chosen for investigation. First, the direction in which the light 

 from the door of the ice-house had illuminated them was clearly 

 marked upon their upper surfaces, and then they were removed to 

 the laboratory and studied by means of transverse hand-sections 

 taken vertically downwards in a direction parallel to the direction 

 of the rays of light which had illuminated them (c/. Fig. 135). The 

 sections, after being mounted in water, were still alive. 



On observing the sections it was found that, in every fruit-body, 

 the ripe asci all across the discs were bent at their free ends in the 

 direction of what had been the source of light. It was thus proved 

 that the asci of Ciliaria scutellata are heliotropic. Some of the 

 hehotropically curved asci are shown in Fig. 135. Each of them is 

 bent terminally through an angle of 45°. 



A mature fruit-body of Ciliaria scutellata, which was about 

 1-25 cm. in diameter, was spread out as a flat disc on a board on 

 the floor of one of the ice-houses over 50 feet away from the doorway 

 through which came the light which had illuminated it unilaterally. 

 I touched the fruit-body and had the satisfaction of seeing that, as 

 it puffed, it shot away its spores in the direction of the source of 

 illumination. The direction of puffing could only have been due to 

 the fact that the asci were positively heliotropic and, during their 

 development, had bent their free ends toward the light. 



The paraphyses of Ciliaria scutellata, as in the Discomycetes 

 generally, come to maturity before the asci, and the asci push up 

 between them (c/. Fig. 135). At first, each ascus is quite straight 

 and the young spores are relatively small with the uppermost one 

 at some distance from the end of the ascus. As a young ascus 

 continues its development, the spores grow in size and move 

 upwards so that the top one of the chain of eight becomes appressed 

 to the operculum, while the ascus as a whole, through increase in 

 length, comes to push its apex about 30 [j, above the general level 

 of the paraphyses. It is during the emergence of the end of the 

 ascus into the free air that the ascus responds positively to the 

 hehotropic stimulus of light, and the actual curvature is confined to 

 the last sixth (40-50 y.) of the ascus length (Fig. 135, h-k). 



