AECHER — ON ZYGOGONIUM. 117 



original cell-contents, though these be poor in endochrome, the central 

 cell containing the spore, takes place. 



Such then being the characters of the genus Zygnema (Ag.) — viz., 

 joints containing two axile, more or less distinctly stellate chlorophyll- 

 bodies, each surrounding a starch granule, and connected by the central 

 nucleus, or in a "resting" condition, becoming so densely filled with 

 endochrome that the stellate appearance becomes lost, zygospores formed 

 either in the connecting tube or in one of the parent cells, and this by 

 the complete fusion of the whole of the cell-contents of the parent cells 

 — such being, I say, the characters of the genus, there can be no question 

 that, relying on the correctness of his description as regards the plant 

 named Zygogonium didymum, de Bary is quite right in making a new 

 genus for the same. All that I venture to deprecate is his not coining a 

 new name for it, in order to avoid ambiguity. 



But, in order to compare our plant with de Bary's, and this for the 

 purpose of showing that they are not identical, it will be advisable here 

 to give de Bary's description of Ms Zygogonium, inasmuch as I believe 

 it does not occur in any English book, and this is as follows :* — 



Cells cylindrical or barrel-shaped, with thick, often many-layered 

 cell- wall, towards the middle at each side an irregular chlorophyll- 

 corpuscle, furnished with a starch granule ; both often confluent into 

 an axile string (in the very thick- walled cells, mostly covered with 

 granules) • union of the conjugating filaments ladder-formed; the pro- 

 cesses of the two cells of the filament, which grow opposite one another, 

 and take up the chlorophyll contents, become shut off as fructification 

 cells, which then become fused together into a non-contracted zygo- 

 spore.! 



The type of this genus so defined is supposed to be the common Z. 

 ericetorum ; but, as it appears, according to de Bary, that the typical 

 Z. ericetorum has not been found conjugated, his allusion to the process 

 in the generic diagnosis is founded on dried examples, from Professor 

 Rabenhorst's collection, of a form named Z. didymum, which he (Pro- 

 fessor de Bary) considers, however, very closely to resemble the water- 

 form of Z. ericetorum. 



Now, my plant (Fig. 1) has short cells, varying in this regard from 

 nearly quadrate to three or four times longer than broad, according to 

 the interval of time elapsed since division ; the contents bright herba- 

 ceous green, forming an axile compressed band, with a central therein 



* " Untersuchungen," &c, p. 79. 



f I would here, as regards this latter character, remind those who may consult de 

 Bary's drawings (1. c.) of his Zygogonium didymum, although his Fig. 18 does not show 

 any granular contents as left behind in the cavities of the parent conjugated joints (as in 

 Fig. 19), that he expressly mentions, in the explanation of the Plate, that in all the 

 cells of these figures " a primordial utricle, with contents, was present, where left out in 

 the drawings" — otherwise, indeed, they could not accord with the character and descrip- 

 tion given of his plant. 



VOL. V. R 



