14 The North American Cup-Fungi 



orderly fashion and the spores are Hterally shot out. Just why 

 so many asci discharge their spores in unison, it is difficult to 

 state except that all naturally respond in a similar manner to 

 the same stimulus. Just what this stimulus is no one has been 

 able to decide with certainty. The contraction of the ascus 

 after rupture would have a tendency to force the spores out. 

 It was at one time thought that the Ascobolaceae ejected their 

 asci but this was a mistake. 



In the larger cup-fungi so many asci discharge their spores 

 at once that it gives rise to a faintly audible puff and is ap- 

 parent 'to the unaided eye as a cloud of smoke (Fig. 7). This 

 phenomenon is well known to all students of fungi but it remained 

 for Mr. W. R. Fisher of Cornell University to photograph the 

 process and to him I am indebted for the accompanying illustra- 

 tion which has been previously published in Phytopathology. 

 A. H. R. Duller believes that puffing does not take place under 

 natural conditions. It is certainly frequently observed in the 

 field although it may be due to unusual disturbance of some 

 kind. 



The force with which the spores are discharged has been 

 indicated by Buller in his " Researches on Fungi " for Ascoholus 

 immersus. His experiments showed that the maximum, height of 

 projection was 35 cm., the violence of the discharge probably 

 not being exceeded by any other ascomycete. 



8. Heliotropism or Phototropism 



While the vegetative stage of the cup-fungi is able to grow 

 in the absence of light, being chlorophylless, the fruiting stage 

 invariably seeks the light and is positively heliotropic or photo- 

 tropic. This is especially apparent in the asci themselves. At 

 maturity, the asci often protrude half their length or more above 

 the surface of the hymenium. This character was at first 

 thought to be restricted to the Ascobolaceae and in fact was the 

 distinguishing character of the family, as at that time known. 

 It is, however, now known to be common to many if not all of 

 the operculate cup-fungi although much more apparent in some 

 than others. It is especially apparent in Ascobolns immersus 

 because of the large size of the spores and asci and the fact that 

 the dark color of the latter renders them more conspicuous by 

 reason of contrast. When grown in the laboratory near the 

 window the asci will be found to bend at a strong angle toward 

 the light. 



