126 ARCHER, ON PALMOGL@A MACROCOCCA. 
resting observations render their truly autonomous character 
doubtful, although I fancy each has been perhaps too hasty 
and too comprehensive in his generalisations. 
Clearly this genus and Cylindrocystis are very closely 
related, and to whatever group one belongs so does the other. 
By Nageli the genus Mesotznium is placed with the Des- 
midiaceze, and by De Bary both those genera are classed in 
that family. By the latter writer the Conjugate are divided 
into three families—Mesocarpex, Zygnemeze, and Desmidiez 
—their distinctions drawn from the mode as to special details 
of the formation of the zygospore and of the development of 
the young plants originating therefrom, distinctions I need 
not more than allude to here. The distinctions based upon 
the fact as to whether all the daughter-cells originating from 
the germ-cell are again capable of self-division, or whether 
one of the daughter-cells remains as a “ root-cell”’ incapable 
of further self-division—the former characterismg the Des- 
midiez, the latter the Zygnemacee—De Bary considers the 
only decided pervading features absolutely separating these 
two families. Mesocarpez are distinguished from both by 
peculiarities in the formation of the zygospore itself. Suffice 
it that the genera in question, as indicated by that author’s 
original researches, in the mode of development, seem to 
accord with the characters in that regard as specially apper- 
taining to the Desmidiacez. 
There is a character, however, which seems to pervade the 
family Desmidiacez, and is certainly demonstrable in every 
undoubted member of the group. I allude to the well-known 
fact that the vegetative increase of a cell, or “frond,” is 
effected by the formation of two new half-cells, which become 
interposed between the older, so that the two newly produced 
cells consist each of a new and old half-cell. Of course a 
figured outline cannot be assumed as an essential, though it 
is very frequent, and affords classificatory characters. 
Is there any evidence of such a mode of cell-increase 
in Mesotenium? I fancy there is. I refer to fig. 6, in 
which the chlorophyll-plate is divided, and a division of the 
cell itself is taking place. Then the two portions of the 
chlorophyll-plate appertaining one to each daughter-cell, in 
place of presenting in side, i.e. edge view, the somewhat fusi- 
form figure, pointed at both ends, which is seen in a fully 
grown cell, now show the end near the septum which halves 
the mother-cell to be bluntly rounded. I conclude, therefore, 
that its recovery of the fusiform and pointed outline at the 
blunt ends may be due to a new growth onwards in that 
direction, therefore accompanied by the growth of a new half- 
