REPEATED ZOOSPORE EMERGENCE IN DICTYUCHUS^ 



William H. Weston 

 (with plate XXIII AND ONE FIGURE) 



DiciyucJius, one of the less known genera of the Saprolegni- 

 aceae, was established in 1869 by Leitgeb (6) to include a single 

 species, D. monosporus; and in 1872 Lindstedt (7) added the two 

 species D. polysporus and D. Magnusii; while in 1893 a fourth 

 species, D. carpophorus, was described by Zopf (12). Leitgeb 

 observed that in his type species laterally biciliate zoospores emerged 

 from sporangiospores which were invariably retained in situ, and 

 that thesp zoospores swarmed but once; and since this condition has 

 been found in all the other species, it has been regarded as charac- 

 teristic of the genus. 



In this paper certain observations on an undetermined species 

 of Dictyuchus are presented, which show that, in this instance at 

 least, the usual history, as described by Leitgeb and others, may 

 be modified through the presence of a second swarming of laterally 

 biciliate zoospores, which occurs after the first has been completed; 

 and since, so far as the writer is aware, a diplanetic condition of 

 this type has not hitherto been noticed in any of the Saprolegnia- 

 ceae, a record of its occurrence has seemed desirable, even before 

 a comprehensive study of the fungus has been completed. 



The Dictyuchus in question appeared in a culture of moist sand, 

 leaves, and other debris taken from a shaded brook bed in a ravine 

 near Great Barrington, Massachusetts; and for over a year and 

 a half it has been kept under observation both in gross and pure 

 cultures, which have been subjected to a variety of cultural condi- 

 tions. During this period, however, all attempts to induce the 

 formation of sexual organs have been without result, although 

 sporangia were readily and abundantly produced, and it is thus 

 impossible to reach any definite conclusion as to its specific iden- 

 tity. That it cannot be referred to D. carpophorus Zopf is evident 



' Contribution from the Cryptogamic Laboratories of Harvard University, no. 85. 

 287] [Botanical Gazette, vol. 68 



