208 ARCHER, ON CYLINDROCYSTIS, 
to his Penium Brebissonii, and of which Dr. Hicks writes :— 
“So far as can be ascertained, Mr. Thwaites calls Cocco- 
chloris Brebissonii, although Mr. Archer thinks he means 
Trichodictyon rupestre (Kiitz.) ; the exact characters of this 
form, it will thus be seen, are by no means settled by any 
one of these observers.””’ Dr. Hicks writes, indeed, “ this 
form ;” but the supposed confusion is partly accounted for by 
the fact, that there are two distinct forms referred to under 
the foregoing names, and two forms which, as I hold, when 
once seen cannot readily again be confounded; for, even 
though the characters assigned to each should not be found 
presenting themselyes in every specimen with absolutely un- 
mistakeable clearness, that is, if unhealthy or deteriorated 
specimens should again come under consideration—yet I 
believe a certain tout ensemble will, even under such circum- 
stances, readily satisfy the eye familiarized with their 
appearance in their ordinary and healthy condition of their 
distinctness inter se. The plants adverted to under the 
names quoted by Dr. Hicks, but adopting here the names 
which I regard as the correct ones, are Cylindrocystis Bre- 
bissonii, Meneghini, and Cylindrocystis crassa, de Bary. Dr. 
Hicks, indeed, says, as I have quoted, that ‘‘the exact cha- 
racters are by no means settled by any one of these observers.” 
I may venture to refer to my own previous efforts to describe 
their generic characters, and I can only appeal therefrom 
directly to the fresh specimens themselves. 
Dr. Hicks writes that—“ The question, first of all, arises, 
how is a single cell to be distinguished from another single 
cell? What reliable characters are to be fixed upon which 
can be considered as of generic value?” If he propounds 
these questions as regards the old genus Palmogleea, or rather 
as regards the three genera already quoted, I should have 
ventured to think that my previous paper was an answer in 
anticipation. Though in a diffuse way indeed, I think the 
descriptions there given may be found to contain the characters 
enabling an observer to decide to which, ¢#f to any, of the 
three genera, Cylindrocystis, Mesotzenium, and Spirotznia, a 
single cell belongs. Dr. Hicks asks—‘‘ How can we tell 
whether it be a fixed form, a separate entity, or merely a 
transitional form of some other growth?” Again I venture 
to reply, if this question be put as regards the forms imme- 
diately under consideration, that I should be disposed to say 
(so far, I think, as our present knowledge goes), that a suffi- 
cient answer is, that they each reproduce their like by a 
conjugative act, thus renewing the species. For, inasmuch 
as conjugation must be looked upon as a true generative act, 
