WITH NOTES ON OTHER SrECIES. 91 



and to attach themselves to them is clearly marked, but does not appear to be so 

 strong and invariably active as it has been said to be by most vs^riters. 



Each oosphere now secretes about itself a delicate cellulose wall, which gradually 

 increases by successive deposits until it attains a considerable thickness. From the 

 time of the appearance of the wall these bodies are no longer oosphcres, but oospores. 

 The fertilization tubes soon begin to fade and finally quite disappear, as do also the 

 antheridia and even the antheridial branches, in some species. 



By the earlier writers it was assumed from the fact of their presence and from 

 the analogy of related fungi, that the tubes are functional organs of impregnation 

 and that an actual fertilization occurs. Some, especially Pringsheim {^o5, '58, '60), 

 argued for the necessity of fertilization. This author at one time ('60) regarded cer- 

 tain peculiar filaments, whose peculiarity was really due to Chytridiaceous parasites, 

 as male filaments of species which have no antheridial branches; but later ('74), he 

 gave up this view and considered plants of the latter sort as parthenogenetic forms of 

 sexual species. Reinke ('69) described uniciliate spermatozoid-like bodies as the fer- 

 tilizing element in S. monoica. These were probably zoospores of Chytridiaceoe. Cornu 

 ('72) assumed and argued for the necessity of fertilization, and maintained the ina- 

 bility of unfertilized oospheres to form ripe oospores. Doubt of the existence of 

 functional sexuality in these fungi was first expressed by DeBary ('81) and was based 

 on his failure to observe any passage of material from tube to oosphere, or even any 

 opening in the tube. Pringsheim ('82) opposed these views very strongly with argu- 

 ments and with an account of observations of the penetration of the oospheres by 

 amoeboid swarmers — " spermamoebse " — developed in the fertilization tubes and set 

 free from them. Zopf ('82) described amoeboid parasites of Saprolegniacece and 

 attributed Pringsheim's spermamoebse to this source. Ward's observations ('83), 

 while not extensive, confirmed DeBary's. The further discussion of the subject con- 

 sisted simply in the maintenance of their former positions by those engaged, and may 

 be followed in subsequent papers of DeBary ('83), Pringsheim ('83, '83a), Miiller 

 ('83), and Zopf ('83). The result has been that the conclusions of DeBary have gen- 

 erally been adopted and made the basis of discussions of the group. The writer has 

 attempted to investigate the question independently in connection with the cytol- 

 ogy of the sexual organs, to which we may now turn. 



The structure and nuclear chano:es of these oro-ans have been studied chieflv in 

 the genera Saprolegnia and Aphanomyces by previous writers, and by the present 

 one chiefly in Achlya Americana and A. ajnculata. The method employed in these 

 investigations has been that of serial sections. Flies well covered with hyphaj of the 

 species to be studied, bearing abundant sexual organs in various stages of develop- 



