GENERAL SUMMARY 461 



and thus to act as a screen in cutting off injurious rays of light from the 

 spores which lie beneath it. 



Pilobolus gives to flowering plants and herbivorous animals nothing 

 in return for their services in dispersing its spores. However, although 

 Pilobolus does not pay for what it receives, it imposes on the organisms 

 which assist it a burden which is so light as to be practically negligible. 



Chapter III. — A new species of Pilobolus, Pilobolus umbonatus, has 

 been described. It occurs on horse dung at Winnipeg and was observed 

 by the late Dr. Roland Thaxter on sheep dung in the eastern part of the 

 United States of America. 



Pilobolus umbonatus, as compared with P. lo7igipes and P. Kleinii, 

 is a smaller and more delicate species. It is easily distinguished from 

 all other species of Pilobolus by its decidedly umbonate sporangium and 

 its minute ellipsoidal spores. With a hand-lens one can readily make 

 out the acutely-pointed umbonate shape of the dried discharged sporangia 

 when these are seen in lateral view. 



A series of critical remarks on the Pilobolidae, made with a view to 

 assisting future workers on this group, has been recorded. 



Pilaira is regarded by the author as a good genus and not as " abnormal 

 material of Pilobolus." 



To the criteria so far employed by taxonomists for distinguishing 

 species of Pilobolus should be added : (1) the exact shape of the sub- 

 sporangial swelling, whether eUipsoid or pjo-iform, etc. ; (2) the ratio of 

 the width of the sporangium to the width of the subsporangial swelling ; 

 (3) the nature of the depressions or wrinkles on dried discharged sporangia 

 when seen in strong reflected unilateral light ; and (4) the nature of the 

 fringe of the sporangium-wall of dried discharged sporangia, in respect 

 to form, colour, and disposition of crystals. 



The spores of Piloboli, when seen in water, are dichroic : they are 

 orange-yellow or yellowish in transmitted light and green in reflected light. 



The form and the variability of the basal swelling of the fruit-bodies 

 of Piloboli have been discussed. 



The width-ratio of the sporangium, i.e. the ratio of the width of the 

 sporangium to the width of the subsporangial swelling, has been measured 

 in Pilobolus longipes, P. Kleinii, and P. umbonatus. 



The pattern on the sporangium of Pilobolus crystallinus, as illustrated 

 by Coemans, van Tieghem, and Zopf, has been treated of. Patterns 

 develop on the discharged sporangia of P. Kleinii, P. longipes, and P. 

 umbonatus as the sporangia dry up and flatten. Studies on the variability 

 of patterns in P. Kleinii and P. loncjijyes have been made. The pattern 

 on a dried discharged sporangium, while fairly constant in its general 

 aspect for each species of Pilobolus, is subject within each species to a 

 large amount of variation in detail. The typical pattern for any par- 

 ticular species ought to be sought for in the larger sporangia rather than 

 in the smaller ones. 



