igig] WESTON— DICTYUCHUS 289 



growth, transfers to stock cultures were made from such myceUa 

 as proved to be uncontaminated. The development of the fungus 

 thus isolated was studied for over a year in Van Tieghem cells, 

 Petri dishes, and battery jars, under a great variety of cultural 

 conditions. 



The mycelium in its morphological characteristics is very simi- 

 lar to that of other species of Saprolegniaceae which have been 

 grown in pure culture. Physiologically, however, it is charac- 

 terized by weak growth, and in consequence requires more fre- 

 quent transfer and more concentrated nutriment for successful 

 maintenance. The process of sporangium formation in its early 

 stages closely resembles that which is usually found in other 

 members of the family. In the young sporangium initials, filled 

 with dense protoplasm, hyaline clefts arise, extend, and divide 

 the contents into subequal, polygonal spore initials. The sudden 

 shrinking of the sporangium with a concomitant vacuolation of 

 the spore initials now takes place; but the vacuolate condition 

 is more persistent than in other genera, since one or two vacuoles 

 are often retained in the spores at maturity. 



In the succeeding stages of its development, however, the 

 sporangium shows itself to be quite different from any other 

 member of the family, save perhaps that of the doubtful genus 

 A planes. During the swelling of the individual sporangiospores 

 which marks the final stage of development of the sporangium, it 

 becomes apparent that the delicate membrane surrounding each 

 spore has become firmly united, not only to the walls of the adja- 

 cent spores, but also to the inner surface of the sporangial mem- 

 brane. This close union of the walls appears to be a fundamental 

 peculiarity in sporangia of the generic type, and sharply distin- 

 guishes it from the abnormal but superficially similar conditions 

 which are occasionally encountered in Saprolegnia, Achlya, and 

 Thraustotheca, when large numbers of spores have failed for some 

 reason to make their escape. We are probably justified, more- 

 over, in accepting Hxjmphrey's (5, p. 81) tentative suggestion 

 that this characteristic obtains throughout the genus. Study of 

 the empty sporangium alone (fig. i) might lead one to interpret 

 its so-called "cell-net" structure as the result of a simple division 



