70 THE SAPROLEGNIACE.^ OE THE UNITED STATES, 



undergo various modifications so characteristic and so related to each other that 

 they furnish the basis for the grouping of the species into a natural series of genera. 

 We pass to a detailed examination of their production and fate. 



The first account to give an approximately correct description of these phenomena 

 was that of Hannover ('42), followed by that of linger ('43). Subsequently Prings- 

 heim ('51) and DeBary ('52) extended their observations, and the subject has been a 

 favorite one down to the present. The formation of a sporangium begins with the 

 gradual cessation of the apical growth of a filament. JS^ow commences an accnmula- 

 tion of protoplasm in the terminal portion of the filament, which usually becomes 

 more or less swollen. IS^o increase in size occurs, however, in the hyphse of 

 Aplianomyces. Finally the end of the hypha is filled with a very dense mass 

 of protoplasm with numerous nuclei, which passes rather abruptly into the thin proto- 

 plasm of the lower part. In the narrow intermediate region between the dense and 

 the thin protoplasm, is formed a clear disk of hyaloplasm, seen as a band in lateral 

 view. Its hyaline character is due to the withdrawal of the aaicrosomes from the 

 originally granular protoplasm of that region. Across the lower surface of this disk 

 is developed a cellulose wall, beginning at the wall of the hypha as a ring and pro- 

 gressing rapidly inward from all sides until the central opening is closed, and a solid 

 wall separates the terminal portion of the thread, as a sporangium, from the remain- 

 der. It has been said that this basal wall of the sporangium is different chemically 

 from the other cell walls of the plant. ]^ot only is this improbable a priori, especially 

 in view of its common fate in Scqjrolegnia, but careful examination shows that it 

 reacts like the other walls with chloroiodide of zinc. As before remarked, Rothert 

 ('88j has observed the occurrence of abundant cellulin granules in the region of the 

 forming wall. Later these cannot be recognized and he suggests that they may 

 furnish material for the wall. The hyaloplasm which thus at first lines the spo- 

 rangial surface of this wall soon becomes again granular by the return of its micro- 

 somes. 



The sporangium thus formed was regarded by earlier writers — ISTaegeli ('47) and 

 others — as a free cell enclosed in the end of the filament. It differs widely in form 

 in the different species, and even considerably in the same species. Commonly it is 

 approximately cylindrical, and may be swollen most at its apical end [Sa2)rolegnia) ^ 

 or in the middle {Aclilya), with a length from six to twelve times its greatest 

 diameter. In Pythiopsis, ThraustotJieca and Apodaclilya pyrifera, the length is so 

 reduced that it becomes short-clavatc or pyriform ; and in some sporangia of 

 PytJiiopsis and in Apodaclilya hrachynenia, the form is quite globular. These con- 

 tracted forms occur also among more typical ones in 8. torulosa. On the other hand, 



