218 ARCHER, ON CYLINDROCYSTIS, 
concatenation of circumstances could, in so diverse localities, 
force a certain supposed gonidium of a lichen or spore of a 
moss now to develop into this well-defined form, now imto 
that. Therefore, if,,on the one hand, such genera, perhaps, as 
Chroococcus, Gleeocapsa, Synechococcus, Gloeothece (in 
Chroococcaceze) and Pleurococcus, Gloeocystis and Palmella 
(in Palmellaceze), seem, from Dr. Hicks’s researches, to be in 
jeopardy, it surely appears to me as yet, not to speak of our 
Sylindrocystis, Mesotzenium, and Spirotznia, that it would be 
an incautious and too hasty conclusion to sweep away all 
“ Palmellacez.’? Mere resemblance is not necessarily iden- 
tity. 
Dr. Hicks puts some queries as to the value of certain 
characters of cells, as affording clues to their affinities—that 
is, as to their use in a classification. Certainly no one character 
can in any case be regarded as decisive, nor is such to be 
expected. A combination of all, however, makes up a certain 
tout ensemble, which often tells us that it is, at least, the same 
form or phase of development one has seen before. 
Size of the cells? It, no dowbt, varies within certain, often 
characteristic, limits. 
Position of nucleus? or of a starch-granule or a “vesicle”? 
The former is seldem discernible, and it can, on that account, 
rarely be of use; the latter, how constant and characteristic 
in certain Desmidians, and many other Confervoids. 
Disposition of chlorophyll? This is in certain stages of 
very many forms a most useful character, e.g. Hormospora, 
Ophiocytium, Conjugatie at large, &c. &c. Dr. Hicks, indeed, 
supposes the case of “ Zygnema”’ (properly Spirogyra), in 
which the contents in conjugating lose their spiral arrange- 
ment, and become “ homogeneous ;” and then he says— 
“ Supposing subdivision to take place, the contents of the 
resulting cells would become more or less homogeneous, and 
thus the spiral character lost.” But this is not what takes 
place. The spore casts off its outer coat, and the inner one 
elongates, of which, upon ‘dividing the upper cell, becomes 
the first ordinary joint of a new filament, and the spiral 
arrangement of the chlorophyll is resumed, the lower remain- 
ing undivided as a “root-cell.”” There is, indeed, more of 
a characteristic uniformity in the disposition of the phyco- 
chrome in the Chroococcacee. 
Form of the cell? This is surely in many instances of the 
greatest value. Dr. Hicks points to the plate illustrating my 
own former paper as an example of the instability of this 
character. But I hardly think it is a conclusive argument 
against the valuc of this character to regard a plant in the 
