PERONOSPORALES 189 



The sexual organs of Albugo, on account of their hidden 

 position in the interior of the host, were discovered much later 

 than the sporangia. They were first noted by de Bary in A. 

 Candida. He saw the penetration of the fertilization tube to the 

 oosphere, but, failing to observe its rupture, felt that it effected 

 fertilization by contact only. His view was doubtless influenced 

 by his earlier work on Saprolegnia where he had found partheno- 

 genetic species. Subsequently, other investigators, using modern 

 cytological technique, have examined A. Candida and several 

 other species of the genus, and have found a true sexuality in all. 

 Their discussions indicate such a great diversity in the details 

 of the sexual process in the different species that the genus must 

 be regarded, from the standpoint of the cytologist, as one of the 

 most remarkable and interesting in all the fungi. It will be 

 necessary to summarize the results on several forms in order 

 to give a clear conception of the situation in the genus as a whole. 



In all of the species the young sexual organs are cut off by 

 transverse septa from the main body of the hypha after the 

 flowing in of the cytoplasm and nuclei. Both organs are multi- 

 nucleate from the beginning. At about the time that the 

 antheridium comes in contact with the oogonium a differentiation 

 of the protoplasm of the latter into a peripheral zone of periplasm 

 and a central spherical oosphere begins to take place. The 

 majority of the nuclei are left within the limits of the oosphere. 



In A. Candida the oogonium contains approximately one 

 hundred nuclei, the antheridium six to twelve, and these undergo 

 one simultaneous division throughout both organs before the 

 oosphere is formed. At the point of contact of the oogonium 

 and antheridium the wall becomes very thin, and the oogonium 

 pushes through forming a slight prominence within the antherid- 

 ium. This has been termed the receptive spot (Wager, 1896 b) 

 or the receptive papilla (Stevens, 1899; 1901). It seems to be 

 functionless, and its formation may be due merely to the existence 

 of a higher state of turgor in the oogonium than in the antherid- 

 ium. It soon disappears, and the fertilization tube from the 

 antheridium enters through the resultant thin spot in the wall, and 

 advances to the oosphere. After completion of differentiation 

 of the protoplasm of the oogonium into periplasm and ooplasm 

 all of the nuclei, both in the antheridium and in the ooplasm, 

 undergo a second mitosis, while those in the periplasm remain 

 inactive and soon disorganize. Coincident with this second 



