SEXUAL REPRODUCTION IN THE BRY8IPHEI. 153 



Underneath this cell, and from the filament which bears it, are seen 

 to spring eight or nine tubes, which join themselves to each other 

 by their sides and to the pedicel of the antheridia, while they apply 



their inner face to the oocyst, above which their extremities soon 

 meet. Each of these tubes is then divided by means of transverse 

 septa into two or three distinct utricles, and in this manner the 

 multicellular wall of the perithecinm Bprings into existence. Dur- 

 ing this time the oocyst enlarges and divides, without its being 

 possible to detect precisely how it happens, into a central cell, and 

 an outer layer, which is ordinarily simple, of smaller utricles con- 

 tiguous to the general enveloping wall. The central cell becomes 

 the single theca proper to the species of Erysiphe of which we are 

 speaking, and the layer which surrounds it constitutes the inner 

 wall of the globose perithecium. The only changes which are 

 afterwards to be observed are the considerable increase of the peri- 

 thecium, by the fact of the development of all its component cells, 

 the production of the radicular filaments which proceed from its 

 outer wall, the brown tint which this assumes, and finally the for- 

 mation of the spores in the theca. The autheridium remains for a 

 long time recognizable without undergoing any essential modifi- 

 cation, but the dark colour which the perithecium assumes finally 

 hides it from the eye of the observer. 



In other species of Erysiphe, oocysts and antheridia, but slightly 

 different in form from those just described, may be seen. The 

 structure of their perithecia, when they are ripe, agrees also as 

 regards the principal characteristics with that of the one we know, 

 only these conceptacles generally enclose several theca?, among 

 which are distributed numerous series and special groups of barren 

 cells. In consequence, the method of division of the oocyst must 

 be much more complex than in Erysiphe dehor acearum, but this 

 phenomenon has not as yet been visible, on account" of the opacity 

 of the young perithecia. Concerning the final structure of the 

 perithecia, the first volume of " Selecta Fungorum Carpologia," of 

 M. M. Tulasne, may be consulted, as also the dissertation published 

 by them in the " Annales."* 



Bonds of analogy, as regards the formation of the perithecia, 

 doubtle;*s unite the genus Eurotium to Erysiphe. As I have shown 

 elsewhere,f ^ ne generative filaments of the perithecia in the Eurotium 

 twist together at their summit like a corkscrew, and generally pre- 

 sent six turns of a screw solidly united to each other, and forming 

 a conical hollow body. After a short time this body is slightly 

 swollen, and composed of a multitude of rounded cells, which even 

 fill it?> central cavity. The most superficial of these cells are again 

 v ry distinctly arranged in spiral series. How the changes and 

 sub-divisions of cells, which bring about this second state of the 

 young perithecium, take place, has not as yet been ascertained ; at 



* " Annales des Sci. Nat.," sec. 4, vol. vi., p. 299. 

 f " Botuuiiche Zeituuy," lor 1854. 



