152 THE SAPROLEGNIACEAE 



branched groups. They are usually a little larger in the distal half, often 

 bent, sometimes branched, of various size, in old cultures often very 

 long, not rarely thread-like with only a single row of spores. They 

 usually break off from the hyphae about the time the outline of the spores 

 becomes distinct and go into a resting state which may last a few days 

 or many weeks depending on conditions. During this time the spores 

 are separated by walls which in this condition are scarcely visible, the 

 individuality of the spores being indicated by the usually conspicuous 

 vacuole that each contains. On emerging the spores escape singly 

 and swim as normal in the genus or they often sprout in position into 

 slender hyphae. Spores Ii.8-i6.6;ji in diameter before sprouting, with 

 large conspicuous vacuole. Oogonia not developed. 



Plentiful in springs and small streams, such as Arboretum spring 

 and brook, Battle's branch, branch back of athletic field, etc. Col- 

 lected 63 times from February, 1912, to December, 1913 (see table on p. 14) ; 

 also found many times since. The plant has a way of appearing tardily 

 and often turns up in old cultures. In our collection notes it often may 

 ha\'e missed being listed, because the culture was not kept long enough. 



The resting stage is not of fixed length, but may be brought to an 

 end at any time by a change of environment, such as by putting a cover 

 glass over a resting sporangium or by a change of water. If the original 

 culture remains undisturbed the sporangia may continue in the resting 

 condition practically indefinitely, that is, for several months. The 

 falling off of the sporangia begins while the plant is still in active growth, 

 and as age approaches the protoplasm may practically all be used up 

 in the formation of such sporangia (see also Weston, '19, p. 290). This 

 deciduous habit is found also in D. monosporus, and is mentioned both by 

 Leitgeb ('69, p. 366) and by Minden ('12, p. 566). According to the 

 former this habit appeared only after cultivating the fungus for two 

 months, but Minden finds it occurring regularly in the same species and 

 does not consider it a result of degeneration. This species has been 

 watched by us for twelve years and though grown on a great variety of 

 media it has never been observed to form oogonia, antheridia, or gemmae 

 other than the resting sporangia, if such might be considered gemmae. 



Of the four described species in this genus our plant seems most 

 like D. monosporus and D. polysporus, the sporangia being exactly as fig- 

 ured by Leitgeb for the former and by Lindstedt for the latter, and in the 

 former, as mentioned above, they tend to fall off in a resting state. There 

 are objections to establishing a species or variety on the basis of the ^•ege- 

 tative and asexual reproductive characters alone, but the very positi^■e 

 sterility of our plant over a series of ten years of cultures in various media, 

 representing over a hundred findings, would seem to justify naming it, if 

 for no other reason than convenience. The same plant to all appearances 

 is found in other places and is probably wide-spread. We take it to be the 



