ARCHER, ON DESMIDIACE.E. 231 



pool the whole of the endochrorne might become used up iu 

 the production of the zoospores, as the course of nature may 

 have been more or less arrested under the conditions to which 

 the gathering had been necessarily subjected. The empty 

 cell- membranes, or old segments, were to be found for some 

 time afterwards in the gathering, when all traces of the 

 zoospores had completely disappeared ; and I may add, that 

 the formation of zoospores occupied only two days when 

 there was a complete cessation of their development. I may 

 also add that the gathering, in which the phenomenon I have 

 been endeavouring to describe occurred, was made in Septem- 

 ber last. 



A glance at the figures will be quite enough, as it seems 

 to me, however imperfect my own description may be, to 

 prove that the phenomenon in question cannot be mistaken 

 for any development of the parasitic growths Pythium 

 entophytum (Pringsheirn),* or of any species of Chytridium 

 (Braun), although a hurried reading might possibly lead to 

 such a conclusion. These organisms consist of colourless 

 pyriform or flask-shaped bodies, with a more or less elongate 

 neck, — in the former instance originating, in greater or less 

 numbers, within the cavity of the cell attacked, and protruding 

 their necks through its external wall, — in the latter, seated 

 externally upon it — and both producing and emitting very 

 minute zoospores through their opened apices. Be these 

 curious growths antheridial structures or true parasites, which 

 latter, I apprehend, is most likely, there does not seem much 

 danger of confounding that form placed under Braun's genus 

 Chytridium with the phenomenon in Docidium above 

 described, but a mistake, so far as regards Pythium ento- 

 phytum (Pringsheim), seems, perhaps, more worthy guarding 

 against. For a figure of tins plant attacking Eremosphcera 

 viridis (De Bary) (= Chlorosphara Oliveri, Henfrey), see 

 ' Micrographic Dictionary/ PI. xlv, Fig. 8. It has, also, 

 been noticed by Carter attacking the cells of Spirogyra, by 

 Brebisson infesting various Desmidiacese, and is sometimes 

 met with in Closterium lunula. In Pythium the several 

 distinct parasites seem to be nourished at the expense of the 

 contents of the infested cell, presently protruding their 

 tubular necks through its boundary wall, outside which they 

 burst at their apices and discharge exceedingly minute 

 " zoospores-/' formed from what has now become their own 

 proper cell-contents, which are not green ; whereas, as above 

 indicated in the phenomenon in Docidium, now here for the 



* ' Anuales des Sciences Naturelles. Bot.,' i Ser., tome xi, PI. 7, fig. 1* 



VOL. VIII. T 



