192 
Wager . — The Life-history and 
The Relationship of Polyphagus to other Forms. 
The Chytridiaceae have not been very exhaustively investigated, and 
very few complete life-histories of them are known. But we have sufficient 
information concerning various members of the group to show that sexual 
reproduction may vary from the simple direct fusion of motile gametes — 
zoospores — to the copulation of non-motile gametes which may be either 
uninucleate or multinucleate and which show clear transitions to the methods 
of sexual reproduction in the higher groups of the Fungi. 
The copulation of motile zoospores has been described by Fisch (’84) 
in Reesia and by Sorokin (’89) in Tetrachytrium . The cytology of these 
forms is unknown. Kusano (T2) has, however, shown that in the new 
species, Olpidium Viciae , which he has discovered, binucleate cells are 
formed by the copulation of motile uninucleate zoospores. Griggs (TO) 
had previously described a new genus, Monochytrium , which in some respects 
resembles Reesia (Atkinson, Bot.Gaz., xlix, 1910) and bears some resemblance 
to the species described by Kusano, the zoospores of which penetrate the 
cells of the host (. Ambrosia artemisiae folia) and there become amoeboid ; 
some of the amoebulae then unite in pairs to form binucleate zygotes. 
In Zygorhizidium Willei , according to Loewenthal (’05), the gametes 
are uninuclear and are equivalent to sporangia. They are placed in 
contact with each other by a copulating tube put out from the smaller, male 
gamete, the contents of the latter then passing over into the female, which 
thus becomes the zygote. 
In Olpidiopsis also it is probable, according to Barrett (T2), that the 
gametes are equivalent to sporangia. Unlike Zygorhizidium, however, the 
gametes are multinucleate and the sexual nuclei probably fuse in pairs, 
presenting thus an analogy with Cystopus {Albugo) Bliti. 
In its general structure and life-history Polyphagus is obviously 
associated with Zygorhizidium, and the cytological structure of these two 
forms, together with that of Olpidiopsis , clearly indicates the connexion of 
the Chytridiaceae with the Oomycetes. But Polyphagus also has some 
relationship with Zygochytrium , a form which possesses a well-marked 
Chytridiaceous sporangium, but is connected with the Mucorineae through 
its Mucor-like formation of zygospores. 
This brief summary shows, therefore, that Polyphagus forms a very 
obvious link between Zygochytrium and Zygorhizidium , and that there is 
clearly a progressive sexual series from Olpidium and Monochytrium 
leading on the one hand to the Mucoraceae through Polyphagus and 
Zygochytrium , and on the other to the Oomycetes through Zygorhizidium , 
Polyphagus , and Olpidiopsis . 
But Polyphagus , and possibly other members of the Chytridiaceae also, 
shows some relationships with the Protozoa. Thus, in its general structure, 
