120 NATURAL HISTORY SOCIETY OF DUBLIN. 



the other hand, this plant shows an affinity to Zygnema, Spirogyra, 

 and Sirogonium ; but it is, of course, completely distinct in its com- 

 pressed band of endochrome, not doubly-stellate, as in the former genus, 

 and not forming a parietal spiral band, as in the two latter genera. The 

 complete emptying out of the conjugating cells in Mougeotia glypto- 

 sperma (de Bary) imparts a peculiar smooth, almost shining aspect to the 

 filaments, which, coupled with the peculiar grooved and ridged spores, 

 gives a mass in the conjugated state a remarkably pretty appearance. 

 Excellent figures of this plant are given by de Bary.* 



In my plant, then, the endochrome forms an axile band, and its zygo- 

 spore is formed by the total fusion of the entire cell-contents of two con- 

 jugating joints into the zygospore within the transverse tube, and without 

 any portion of the contents being shut off from the spore in the cavities 

 of the parent joints. This plant is not a Mesocarpus, being quite ex- 

 cluded from that genus for the last reason mentioned. It is in truth a 

 Mougeotia, in the de Baryan, but not the Agardhian sense. It is to be 

 distinguished from Mougeotia glyptosperma (de Bary) by its much shorter 

 and wider cells, much wider transverse tubes, by its cells not becoming 

 kneed or curved during conjugation ; but pending conjugation present- 

 ing (as before mentioned) the appearance of a perforated ribbon-like 

 structure, not a wide-looped network ; and, above all, by its zygospore 

 being simply elliptic, and destitute of the grooves and ribs, and the some- 

 what acute keel, which form so distinguishing features of that of M. 

 glyptosperma. 



But a further reason for bringing Zygogonium (de Bary) into the 

 question in connexion with this plant, besides its no doubt considerable 

 general resemblance thereto, is that at certain stages of the process of 

 conjugation the present plant presents appearances so like de Bary's 

 figure,! but perhaps still more like Kabenhorst's, as to lead to the view, 

 as before mentioned, that it and they may be congeneric, notwithstand- 

 ing that de Bary made a separate genus of his plant. 



This circumstance alluded to is a standstill, as it were, sometimes 

 noticeable, of the globular mass of the contents of each parent joint, just 

 within the connecting tube, where they became definitively bounded, 

 to appearance, as if distinct individualized cells, ultimately, however, 

 coalescing to form the zygospore (Fig. 3). 



Now, the question arises — May de Bary's figures (it will be noted 

 made from dried specimens) have been possibly taken from examples 

 arrested at this stage of advancement of the process of conjugation, and, 

 from the same cause — that is, dried and deteriorated specimens — may 

 he not have supposed these bodies, thus partially advanced towards 

 conjugation, to be portions only, not the total cell-contents, wholly re- 

 tracted from the cell- wall ? May some external granules have lent to'the 

 specimens an appearance of certain granular contents left behind within 



* Op. cit., t. viii., %g. 20, 21, 22, 23, 24, 25. 

 f Op. cit., t. viii., f. 18, a, b. 



