116 NATURAL HISTORY SOCIETY OF DUBLIN. 



transverse tube, in one genus — Zygnema. I have said that Kiitzing 

 seems to have intended his genus Zygogonium to include those Zygne- 

 mata in which the zygospore is formed in the transverse tube ; but, no 

 doubt, he further includes some forms in that genus in which the conju- 

 gated state has not yet been seen. As to such it is manifestly prema- 

 ture to judge ; therefore, upon what grounds he assumes their genus it 

 is not easy to perceive, seeing that his essential generic distinction does 

 not depend on the character presented by the barren state. But as re- 

 gards those whose endochrome is not doubly-stellate, but in a single 

 compressed mass or band, and whose conjugated state is also unknown, 

 it is still less easy to see why he places them in the same genus. If, as 

 I should think, in accordance with de Bary, we ought to do, we place 

 all the forms with the doubly- stellate arrangement of the endochrome in 

 the genus Zygnema, then such forms, at least (be they all truly distinct 

 or not), as Kiitzing' s Zygogonium conspicuum, Z. decussatum, Z. affine, 

 Z. parvulum, Z. immersum, Z. cequale, Z. nivule, Z. lutescens, Z. anoma- 

 lum, and others, are to be considered as belonging to Zygnema. Zygo- 

 gonium pleurospermum (Kiitz.) has been shown by de Bary to be truly 

 a Mesocarpus (just as the false genus "Rhynconema" is strictly refer- 

 rible to Spirogyra). There then seems to remain, perhaps, such forms 

 as Zygogonium ericetorum (Kiitz.), Z. torulosum (Kiitz.), and Z. Iceve 

 (Kiitz.), of the forms enumerated by Kiitzing, which cannot be referred 

 to Zygnema, judging even from their barren state. And it is for such 

 forms as these last mentioned, with quite another mode of conjugation, 

 according to de Bary, that the latter would make a genus under the same 

 name, having removed to the genus Zygnema, as before mentioned, 

 the other forms referred by Kiitzing to his Zygogonium. 



"Why Kiitzing should have placed a plant like his Zygogonium lave, 

 with its axile bands of endochrome quite unlike the forms with the ar- 

 rangement of the contents as in Zygnema, in the genus Zygogonium at 

 all, the more especially as he was unaware seemingly of the conjugated 

 state of this form, seems to me not readily to be perceived. 



Now, having supposed all the forms possessing the arrangement of 

 the endochrome in the unconjugated joints which I have characterized as 

 " doubly- stellate," whether the zygospore be formed in the parent joints 

 or in the transverse tube, as collectively included in the genus Zygnema, 

 it is proper to allude to a common character which pervades the whole 

 of the forms alluded to, and which belongs to them, in common with the 

 other genera of the Zygnemese (de Bary), as compared with the Meso- 

 carpese (de Bary). I allude to the zygospore being the result of the 

 fusion of the entire cell -contents, " primordial utricle" and all, of the 

 pair of conj ugating joints, the spore not becoming shut off from the 

 original common cavity formed by the fusion of the two united parent 

 cells, thus not cutting off portions of their contents very poor in endo- 

 chrome. This may be said to be but a negative character ; but it well 

 distinguishes these from the Mesocarpese, in which latter this dividing- 

 off of portions of the common cavity formed by the union of the pair of 

 conjugated joints, and therewith likewise shutting off portions of their 



