118 ARCHER, ON PALMOGL@A MACROCOCCA. 
seen, it occupies in each a place near the septum ; by and by, 
each is again found at the middle of its chlorophyll-plate, both 
as regards the longitudinal and transverse diameters. Re- 
production in this genus, as in Cylindrocystis, is by conjuga- 
tion and evolution from the spore-cell, in germination of four 
young cells identical with the parent.* In this genus, 
however, the foregoing characters are in some species often 
not easy of application, owing to the density of the granular 
cell-contents obscuring a proper view of the internal struc- 
ture, and to the specimens not being in a conjugated state. 
Such, as briefly as I can convey it, is some account of the 
genus Mesotenium (Nag.), the last of the genera into which 
Palmogleea (Kiitz.) seems capable of being divided. Un- 
doubtedly the three principal, and those most nearly related 
to each other, are Spirotenia, Cylindrocystis, and Mesotz- 
nium; the two others above alluded to should, so far as I can 
judge, have never found a place in Palmoglea. Of these 
three, Spiroteenia may, I think, be said (as far, at least, as 
regards the forms themselves) to bear a relationship to 
Spirogyra similar to that which Cylindrocystis bears to 
Zygnema, and possibly Mesotenium may be considered 
to possess, in a great measure, a relatively similar relationship 
to Mesocarpus or to Leptocystinema (mihi). 
The query with which I commenced this paper suggested 
itself to me after having searched for and having tried to 
examine our Dublin forms included in Kiitzing’s genus, and 
upon a reperusal of Alex. Braun’s remarks,* where that 
author observes that “the species of the genus Palmogleea, as 
established by Kiitzing, cannot be certainly determined 
either by the characters given in ‘ Species Algarum,’ or by 
the figures given in ‘ Tab. Phyc.’””? And he goes on to sa 
that im the species represented by himself, which, doubtfully, 
he calls P. macrococca, “ the jelly-like envelopes are some- 
times distinguishable singly, sometimes not, which renders 
doubtful even the section in which we are to seek the 
species ;” and he afterwards expresses an opinion that several 
of the species (citing six) will have to be combined as forms 
of one and the same species. With that writer I must 
concur in admitting the difficulty of identifying Kiitzing’s 
forms, as well as even the uncertainty, as I before indicated, 
in deciding the section in which we are to seek a particular 
species. But I think it must be admitted that, seizing upon 
other distinctions than those put forward by Kiitzing, abun- 
dantly distinguishable forms, even generically separated, here 
* De Bary, op. cit., p. 34, t. vii, 20—29. 
7 Op. cit., p. 327. 
