ON SEXUAL REPRODUCTION IN THE TEIlONOSPORiE. 151 



accumulated granules of fatty matter. This mass is what I call 

 the gonosphere. Immediately this is formed, the antheridium 

 emits from its contiguous side a tabular and slender process, a sort 

 of beak, which pierces the membrane of the oogonium, and reaches 

 the gonosphere, crossing the ambient plasma. As soon as this 

 fecundating process has touched the surface of the sphere in ques- 

 tion, it no longer increases, but the latter becomes enveloped in a 

 fine membrane of cellulose, and takes all the characteristics of an 

 oospore. 



The antheridium is at first filled with a rather dense protoplasm, 

 which, at the moment of fecundation, often represents a rounded 

 central sphere, from which slender processes radiate in all directions. 

 This appearance is preserved before and after fecundation, and even 

 until the perfect maturity of the oospore. The extremity of the 

 fecundating canal remains closed, and is intimately joined to the 

 membrane of the oospore. There is no appearance of spermato- 

 zoids. The mode of action of this fecundating tube on the gono- 

 sphere may then be compared to the pollen tube in phanerogamic 

 plants. The cellulose membrane with which the oospore is en- 

 veloped then becomes thicker, and finally its endospore is a solid 

 inner integument, made up of several superimposed layers. At the 

 same time there is formed outside, and around this interior cell, a 

 second protecting membrane, which is ordinarily resistant, and is 

 the epispore. This gradually passes from brownish yellow to a 

 darker tint, and is finally ornamented on its surface, according to 

 the species of Peronospora, with warts, folds, filiform and articu- 

 lated prominences, &c. In Cystopus the epispore is made up of 

 encrusted cellulose. This outer tegument is formed at the expense 

 of the peripheric plasma of the oogonium, which is by degrees 

 precipitated on the oospore, and assumes consistency. The ripe 

 oospore occupies the centre of the oogonium, in the midst of a fluid 

 of an aqueous nature, and only holding in suspension a few scat- 

 tered granules. As regards the wall proper of the ripe oogonium, it 

 is, according to the species of fungus under consideration, either 

 very much thickened and rigid, or thin and somewhat evanescent. 

 The endospore finally surrounds a finely granulated plastic layer, 

 which forms, as it were, an envelope around a large central vacuole. 

 The fecundating tube remains recognizable until the maturity of 

 the spore, and it is generally covered by a case, which, proceeding 

 from the epispore, extends as far as the side of the oogonium. 



The oospores of the Peronosporce germinate after a prolonged 

 repose, which lasts at least as long as the winter. As yet two 

 modes of germination are known; in the Cystopus candidus the 

 endospore becomes swollen with its contents under the influence 

 of water, then the epispore bursts at one point, and allows a broad, 

 short, obtuse hernia to issue. Then large and changing vacuoles 

 are observed in the protoplasm, then it divides simultaneously into 

 a multitude of equal parts, which soon become so many zoospores, 



