ZOOLOGY AND BOTANY^ MICKOSCOPY, ETC. 233 



oogonium, before and during the rounding off of the oospheres, is 

 much more coarsely granular and hence less transparent than in 

 Saprolegnia. The oospheres are smaller ; their number always two or 

 more. No opening of the fertilizing tube is apparent, and its contact 

 with the oosphere is less intimate than in Saprolegnia. The oospheres 

 sometimes become invested with a cell-wall when the antheridia have 

 not put out any tubes. 



De Bary describes a new species A. spinosa, nearly allied to 

 A. cornuta, and presenting a very close resemblance to Saprolegnia 

 asterophora. It is characterized by the rarity of the production of 

 reproductive organs, especially of zoosporangia. Ripe oospores are 

 occasionally produced without contact from antheridial tubes. 



Aphanomyces scaher presents no special point of difference from 

 the other genera of the family as regards the mode of reproduction. 

 The oospores are here also sometimes produced parthenogenetically. 



In all the genera described, with the exception of Achlya, the 

 structure of the ripe oospore is the same, having a wall consisting of 

 a thicker epispore and a thinner endospore, which encloses a peripheral 

 layer of granular protoplasm, interrupted by a clear speck, and 

 globules of oil. In Achlya there is no " fertilization speck." In all, 

 the oospore is often matured without the production of antheridia and 

 fertilizing tubes. In Pythium, Phytophthora, and Peronospora, there 

 is a distinct " periplasm." In Achlya, when germination begins, the 

 globule of oil has altogether the appearance of a granular ball of 

 protoplasm. The germinating tube is clothed with a prolongation of 

 the innermost layer of the wall. The entire elongated oospore then 

 becomes a zoosporangium ; or the germinating tube does not directly 

 produce zoospores, but, on reaching a suitable substratum, developes 

 into a vegetating thallus of normal size and form, which then produces 

 both zoospores and oogonia ; or it may branch and produce several 

 zoosporangia. In some species all three modes of germination occur, 

 while others are limited to one of them. 



De Bary considers that the Peronosporeee and Saj)rolegniefe must 

 be retained as two distinct groups, with this as their essential distinc- 

 tion. In the former the oosphere is formed out of a part only of the 

 protoplasm of the oogonium, and is fertilized by the evident absorption 

 of a portion of the protoplasm which passes out of the antheridium ; 

 while in the Saprolegnie^ the oosphere or oospheres are formed out of 

 the entire protoplasm of the oogonium ; their actual fecundation by 

 contact with the contents of the antheridium has in no case been 

 detected, and in some cases certainly does not take place. The 

 original Pythium monospermum of Pringsheim does not agree with the 

 above character, but no doubt from error of observation. 



The genera will then be arranged as follows : — 



I. Peronospore^. Pythium or Artotrogus (including Cystosiphon 

 Cornu), Phytophthora, Peronospora (including Basidiophora Cornu), 

 Sclerospora Schrot., Cystopus. 



II. Saprolegnie^. Saprolegnia ( = Biplanes Leitgeb), Bictyuchus, 

 Achlya, Aphanomyces. 



Of the Peronosporeae, Phytophthora comes nearest to the Sapro- 



