SPORE DISCHARGE AND DISSEMINATION 339 



dissemination of its spores. These include (1) the dependence upon Hght 

 for the production of sporangia, (2) the positively phototropic response 

 of the sporangiophores (see frontispiece), (3) the violent discharge of the 

 sporangium into the air toward the source of light, (4) the sticky nature 

 and the heavy black wall of the sporangium, and (5) the dissemination 

 of the spores by the passage through the digestive tract of animals which 

 ingest them. 



We owe much of our knowledge regarding the structure of Piloholus, its 

 physiology, and its life history to the careful study and comprehensive 

 descriptions of Buller (1934). Much of his work was done with P. kleinii 

 and P. longipes. Brefeld (1881) showed that, in the absence of light, no 

 sporangia were formed, but that the sporangiophores continued to grow 

 for 10 to 14 days and reached the length of 8 to 10 in. A 2-hr. exposure to 

 light was sufficient for partially formed sporangiophores to complete their 

 development in the dark. Sporangiophores and sporangia developed 

 normally in blue light but did not develop in red-yellow light. 



Under natural conditions, Piloholus produces successive daily crops of 

 sporangiophores and sporangia. Each crop requires approximately 24 hr. 

 for its development. The sporangiophores begin to form near midday 

 or early afternoon. By evening they have received enough light to allow 

 the further development and production of the sporangia during the 

 night. By the following morning, the sporangia are completely formed. 

 During the morning the sporangiophores react phototropically, directing 

 the sporangia toward the source of light. From midmorning to early 

 afternoon the sporangia are discharged violently into the air for a con- 

 siderable distance. The horizontal distance, according to Buller, may 

 be as great as 8 ft. 7 in. 



To understand the mechanism of sporangium discharge in Piloholus, it 

 is first necessary to know the structure of the sporangium and the spo- 

 rangiophore (Fig. 69). The entire sporangiophore consists of a single 

 large cell, with a rather slender lower portion, a subsporangial swelling, 

 and a conical columella, which projects upward into the sporangium. A 

 rather thin layer of cytoplasm lies next to the cell wall and surrounds a 

 large central vacuole. At the base of the subsporangial swelling there is 

 a thick perforated ring of protoplasm, which is reddish in color, containing 

 carotene. 



When the sporangiophore is pointed directly toward the source of light, 

 the parallel rays of light which strike the black hemispherical sporangium 

 are screened out. The subsporangial swelling acts as a lens, and the rays 

 falling upon it are bent so that they converge on, or uniformly near, the 

 red mass of protoplasm at the base of the swelling; this results in an 

 equilibrium, i.e., no bending occurs. When the sporangium is directed 

 at an acute angle away from the source of light, the side of the sub- 



