34 DtTBLIN NATURAL HISTORY SOCIETY. 



zoospores, in every way comparable to the similar bodies found in other 

 algee (Fig. 4) ; their principal distinction from those, for instance, in Cla- 

 dophora, being their temporarily abiding in a cluster, each encysted in 

 its special coating. I vainly tried to satisfy myself whether these zoos- 

 pores were one or two-ciliated, but I was not able to decide this dif&cult 

 point. They were about 1 -3600th of an inch in their narrower diame- 

 ter, and somewhat greater longitudinally. Having, one by one, es- 

 caped, the vacated cells remain not long attached at the apex of the la- 

 teral tube, and I think they fall away therefrom sometimes in a more or 

 less connected condition, and finally decay. The old frond now gene- 

 rally separates at the suture, one segment bearing away the empty spe- 

 cial structure described, the other, of course, unchanged ; any remain- 

 ing endochrome by this time being quite brown, broken up, and dead, 

 if indeed it be not altogether vanished (Fig. 4). I imagine it may be 

 possible that in the native pool the whole of the endochrome might be- 

 come used up in 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 ga- 

 thering, 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 September 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 phe- 

 nomenon in question cannot be mistaken for any development of the 

 parasitic growths F^jthium entopkjtum (Pringsheim), 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 con- 

 founding that form placed under Braun's genus Chytridium with the 

 phenomenon in Docidium above described, but a mistake, so far as re- 

 gards Pythium entophytwm (Pringsheim), seems, perhaps, more worthy 

 guarding against. For a figure of this plant attacking JSremosphara 

 viridis (De Bary) (= CMorosplKBra Oliveri, Henfrey), see " Mi orographic 

 Dictionary," PI. xlv., Fig. 8.* It has, also, been noticed by Carter 

 attacking the cells of Spirogyra, by Brebisson infesting various Desmi- 

 diac£B, and is sometimes met with in Closterium lunula. In Pythium 



* " Annales des Sciences Naturelles Bot.," 4 Ser., tome xi., PI. 7, fig. 1. 



