﻿1903] OOGENESIS IN SAPROLEGNIA 345 



the Peronosporales, are very much in advance of the sexual organs of 

 Monascus, Dipodascus, and Eremascus. 



Barker suggests that the egg of the Peronosporales may be cut out by a 

 •' film of kinoplasm derived from the spindles of dividing nuclei at the period 



i of oogenesis called zonation. He compares this free cell formation to sporo- 



genesis in the ascus, in an attempt to relate the ascus to the zoosporangium 

 through a gametangium which is homologous with the latter. Stevens and I 

 studied carefully the origin of the egg membrane in Albugo and came to the 

 conclusion that its formation has no connection with spindle fibers. In the first 

 place, zonation is not universal among the Peronosporales; and again, it is 

 largely a matter of chance that the nuclei are in mitosis at that time. Then 

 too, the differentiation of the ooplasm is intimately connected with general 

 * dynamic activities of the cell, the same activities that develop the coenocen- 



trum, Zonation is an incident to these more fundamental events. Ooplasm 

 is dense or alveolar, while periplasm becomes very coarsely vacuolate because 

 practically all of the large vacuoles are forced to the periphery by the accu- 

 mulation of ooplasm around the coenocentrum. The plasma membrane 

 which delimits the ^g^ is formed around the dense ooplasm and becomes 

 bounded by the large vacuoles outside. It is probable that this area of kino- 

 plasm splits along a line of vacuoles between the ooplasm and periplasm and 

 the cell wall is deposited between the two opposed plasma surfaces. These 

 add secondary layers to both sides of the primary wall. The differentiation 

 of the ^^^ then bears no resemblance to the cutting out of ascospores by 

 aster fibers, but on the contrary, recalls and agrees with the activity of 

 vacuoles during the segmentation of the protoplasm in the sporangium of 



angi 



We 



the zoosporangium as the possible homologue of the ascus. It should also 

 be noted that the preliminary fusion of nuclei in the ascus is a peculiarity 

 that cannot be lightly passed over in comparisons of this character, where 

 agreement in cytological detail is absolutely necessary to establish homolo- 



gies. 



It is difficult to handle Dipodascus (Juel, 1902) at present because some 

 details of nuclear activities are lacking both at fertilization and during 

 sporogenesis. It seems probable that the development from the fusion cell, 

 which is essentially a zygote, is sporophytic in character and may look 

 forward to the formation of ascogenous hyphae and asci, in which case more 

 information on the methods of spore formation is much to be desired. 



The writer sees much in the conditions in Monascus and Dipodascus to 

 support his view that the ancestral sexual organs of the Ascomycetes were 

 coenogametes of the type ^illustrated by the molds; that the ascocarp is a 

 sporophytic development entirely independent of possible analogous genera- 

 tions in other groups of fungi (^, ^., the so-called promycelium of /'//j/^//^- 

 thora omnivora)\ and that the ascus is a new form of sporangium, connected 



