SAPROLEGNIALES 155 



Trow believes that they constitute evidence of a true fertihza- 

 tion. He states that one of the nuclei in each binucleate oosphere 

 is a male nucleus introduced by an antheridial tube. He says 

 that while the fully formed naked oosphere is uninucleate, young 

 oospores with very delicate membranes contain two nuclei one 

 of which is often found in the periphery near the fertihzation 

 tube, and older oospores with thicker membranes each contain 

 a single large central nucleus. 



It is generally known that certain species of the group are 

 apandrous, the antheridia never being formed, and even Trow 

 agrees that in such cases fertilization does not occur. In the 

 light of the fact that degeneration of the typical sexual process 

 appears to be taking place in various groups of the fungi, it seems 

 not illogical to conclude from the data at hand that conditions 

 differ in different species, and to agree with the conclusion of 

 Trow that some species {S. dioica) are typically sexual, others 

 (*S. thureti) obviously apogamous, while between the extremes 

 intermediate conditions exist. In recent years a true fertiliza- 

 tion has been described by Claussen (1908) for Saprolegnia 

 monoica, by Miicke (1908) for AcJilya -pohjandra, by Patterson 

 (1927) for Achlya colorata, and by Kasanowsky (1911) for 

 Aphanomyces laevis, while in the related groups, Pythiaceae, 

 Leptomitaceae, and Peronosporaceae, the antheridia apparently 

 function in all cases. 



In apogamous species the spores developed in the oogonium 

 might well be termed aboospores since they correspond to the 

 azygospores of the Zygomycetes. The number of oospores in 

 an oogonium is extremely variable in some species while rather 

 constant in others. In certain species of Saprolegnia and Achlya 

 an oogonium not infrequently contains fifty or more oospores, 

 though the number is usually much less. In the genera Pythiop- 

 sis, Dictyuchus, Aphanomyces, Brevilegnia, Geolegnia, and 

 Leptolegnia a single oospore is usually developed, these genera indi- 

 cating in this respect evolution toward the condition in the 

 higher Oomycetes. After a period of rest germination of the 

 oospore occurs. The inner membrane of the spore is pushed 

 out through a crack in the outer wall and develops into a germ 

 tube. This tube may come into contact with available nutri- 

 ment, put out rhizoids, and develop directly into a new plant. 

 More often after a brief period of elongation it cuts off at its 

 apex a sporangium typical of the genus, and forms sporangiospores. 



