<5(JS BOTANICAL GAZETTE. 



forth a new filament; in the third the conidia send out filaments 

 directly from the apex; and in the fourth they produce filaments 

 from any part of the surface but especially laterally. These sub- 

 divisions are based on physiological rather than morphological 

 grounds, it will be seen, but it may be added that there is a more 

 or less closely corresponding morphological difference. In the 

 first subdivision with zoospores the ramification of the conidio- 

 phores is pinnate, if we except the anomalous P. entospora, which 

 does not branch at all, and the minute P. pusilla, which can 

 hardly be said to branch. The second division includes only 

 two small species in which the ramification is not well marked. 

 The third and fourth divisions run into one another, since the 

 species of the latter sometimes germinate at the tip. As it is, 

 the third division includes only one but a very distinct species 

 where the ramification is dichotomous, but the tips are swollen 

 and bear a number of radiating sterigmata. The species of the 

 fourth and largest division are dichotomous and in several cases 

 so much alike that they can hardly be distinguished by the con- 

 idiophores alone. The haustoria of the different sections are, to 

 a certain extent, characteristic. In the first section they are of 

 the spheroidal type, while in the last two sections they are gen- 

 erally filiform or club shaped, and frequently branch. A species 

 of Peronospora can be said to be satisfactorily known only when 

 both conidia and oospores have been observed and the germina- 

 tion of the conidia ascertained. The germination of the oospores 

 has been seen only in a very small number of species, and this 

 element can not be used in the systematic classification of the 



genus. 



In spite of the small number of known species of Cystopus, 

 our species, it must be confessed, are as yet unsatisfactorily 

 known. This arises principally from the fact that the conidia 

 alone are not sufficiently characteristic, and on several hosts 

 oospores have not yet been found. In some of the species the 

 conidia are all alike in shape, and in germinating they give off 

 zoospores. In others the terminal conidia of the chains differ in 

 shape from the rest, and are said, on the authority of Tulasne, to 

 germinate by means of an outgrowing tube instead of by zoo- 

 spores. The conidia of species of Cystopus are of two types, the 

 spherical and the cylindrical, or cuboidal as they are sometimes 

 incorrectly termed, but, without a knowledge of the oospores as 

 well, it is evident that one can not safely unite forms on widely 

 different hosts, guided only by the ill-marked distinctions- 

 afforded by the conidia. 



