1 14 THE SAPROLEGNIACEAE 



sporangia are abundant. The species is named for the nebula in Orion, which 

 a photograph of the magnified culture somewhat resembles (see pi. 34). 



The following series of experiments were made to test the effects 

 of different temperatures on growth and reproduction. All cultures 

 were made from strains descended from a single spore (from No. 6 of 

 September 26, 1919). Inoculations were uniformly made by cutting 

 out near the periphery of the mycelium small squares of corn meal agar, 

 on which the fungus was actively growing, and placing on these squares 

 termite ants, flies, or vegetable media, etc., for food. Distilled water 

 was used unless otherwise stated. 



Culture on fly, healthy, and just beginning to form sporangia and oogonia was put in 

 electric incubator, temperature 40° C. Examined twenty-three hours later and found 

 to be dead. Repeated with same result. 



Check culture on fly left in room, temperature 21.5° C. Formed many normal asexual 

 and sexual reproductive organs. Repeated with same result. 



Culture on mushroom grub in sterilized spring water was put in incubator at tempera- 

 ture of 36° C. Examined two days later: mycelium thick, long (l cm. from host), 

 mostly straight but some slightly wavy hyphae. Threads unusually densely filled 

 with protoplasm. No sporangia. A good many oogonial initials. No harmful effects 

 of bacteria observed. Reexamined twenty-eight hours later: mycelium still growing 

 vigorously. No sporangia formed. Many oogonia formed, a majority of which had 

 queer stalks which wer every long and coiled like a cork-screw (see pi. 35, fig. 8). In 

 most cases at tips of these stalks abortive attempts to form oogonia were made, 

 resulting, as a rule, in from one to three swellings. 



Two check cultures under same conditions as above, except in room temperature of 20 

 C. Growth normal, many sporangia and oogonia formed during the third day. 



Culture on piece of boiled corn grain embryo was put in incubator at temperature of 

 36° C. A few sporangia produced, some of which emptied normally, others did not 

 empty, though spores were formed. As compared with cultures in room temperature 

 a very small number of oogonia were produced, and about l out of 10 of these formed 

 eggs which had the appearance of being normal. About a third of the oogonia had the 

 curiously coiled stalks as cultures on grub at same temperature (above). Antheridia 

 usually of normal shape on normal oogonia, but on oogonia with coiled stalks anther- 

 idia also coiled. Repeated with essentially the same results. 



Culture on piece of boiled corn grain endosperm (horny and starchy) was put in incubator 

 at temperature of 36° C. Sporangia produced in abundancp, many emptying normally; 

 others forming spores which encysted within the sporangium. Compared with 

 cultures in room temperature a considerably larger number of normal oogonia with 

 good eggs were formed, and compared with culture in incubator on termites a 

 smaller number of oogonia with coiled stalks were formed. This culture approached 

 far nearer in appearance the normal room cultures than any yet cultivated in oven. 

 Repeated with same results. In one of these cultures two little bits of the starchy 

 part of grain, size of pin head, broke off and were inoculated by spores. Both formed 

 tiny cultures about 3 mm. across. The hyphae were very delicate, about one-third the 

 normal diamater. The sporangia, produced in plenty, were mostly relatively as small. 

 The spores, however, were normal size, 9-1OM in diameter. A good many oogonia 

 produced of normal size (50-80^), with eggs equally normal (average 33m). 



