INHIBITORY EFFECT OF LIGHT 109 



necessity arise only on the under surfaces of the dung-balls, but 

 arise just as freely upon the upper and lateral surfaces. Since the 

 force of gravity acts equally well in darkness and in daylight, it is 

 evident, by comparing the results of Culture C with those of Culture 



Fig. 61. — Coprinus sterquilinuts. Culture C, grown in complete darkness. Fruit- 

 body rudiments can be seen on the top and sides of the horse dung. Two 

 perfect fruit-bodies (in the foreground) are developing from rudiments which 

 were at the bottom of the dung, and one perfect fruit-body (in the distance) 

 from a rudiment which was at the top of the dung. Owing to the absence 

 of light the solid stipe -bases have become very long and project above the 

 surface of the horse dung, while the pilei which cap them have remained up to 

 the present relatively small. CJ. Fig. 59, B, which shows a fruit-body of the 

 same age grown in the light. Photographed 23 days after the culture was 

 started from mycelium. Natural size. 



A, that the low position of origin of the rudiments which develop 

 into mature fruit-bodies in top-hghted cultures is decided not by 

 the action of gravity but by that of hght. 



In the Culture D, where the maximum amount of dayhght was 

 brought to bear upon every part of the surface of each dung-ball, 

 a number of rudiments of fruit-bodies appeared at the top, bottom, 

 and sides of the balls ; but they soon ceased to grow and became 

 aborted. Ultimately, however, two rudiments which had evidently 



