457 



by transverse walls into a series of cylindrical cells, each of which repre- 

 sents an antheridiuin. In baprolegma dioica the whole of the protoplasm, 

 of the antheridium separates into numerous minute spermatozoids, which 

 are discharged in a motile state from an opening in a narrow protuberance 

 of the wall of the antheridium. In Ac/ilya dioica the contents of the 

 cylindrical antheridium are divided into a number of portions (of about the 

 size of the zoospores of the species). These in their turn break up into 

 small spermatozoids, which emerge first from their special mother cells 

 and then from the antheridium, in the same way as in Saprolegnia dioica. 

 The spermatozoids of both species move by means of a long ciliurn. It is 

 to be assumed, from the analogy of closely related Algce, that the spermato- 

 zoids enter through the holes in the walls of the oogonia and fertilize the 

 globular bodies by union with them; but there is not enough direct evi- 

 dence to warrant more than an assumption. 



The ripe oospores of Sap'oleynia (so far as they are yet known) possess 

 a membrane consisting of two coats, and produce germ-tubes after a period 

 of rest. They have also been known, but exceptionally, to produce zoo- 

 spores after a short period of rest. 



Suborder 2. PERONOSPOREJE. Fungi parasitic on living Phane- 

 rogams, and consisting of a mycelium of densely ramifying hyphae, 

 which bears both sexual organs autheridia (male organs) and 

 oogonia (female organs) and asexual conidia. They resemble 

 strongly the preceding family, SSaproley niece. The mycelium which 

 rauiihes within the host-plant nrst bears the conidia either singly 

 on branching tree-like (Peronovpora), or in a vertical series on club- 

 shaped (Cy stop us) conidiophores, which appear upon the surface of 

 the affected part of the host-plant. According to the species the 

 conidia are either simple spores, which reproduce the mycelium by 

 emitting germ- tubes directly, or zoosporaugia (as in certain species 

 of Perouospora, Phytophthora infestans, and Cystopus}, the germi- 

 nating zoospores of which give rise to a new mycelium. This new 

 mycelium in both cases produces conidia again, and later the sexual 

 organs. The germinating oospores also produce a mycelium, which 

 bears both conidia and, afterwards, the sexual organs. The asexu- 

 ally-produced conidia here (like the zoosporangia in the Saproley- 

 niece) are functionally of equal value with the sexually-produced 

 oospores. 



Oospores 



Conidia Oospores 



Conidia, Oospores. Conidia, Oospores. 



ILLUSTRATIVE GENERA : Peronospora, Cord. ; Phytophthora, De Bary ; 

 Cystoptts, Lev. 



Structure and Life-history. The reproduction of the Peronosporce so 

 strongly resembles that of the monoecious forms of tlie Saproleynie<* that 



