MESOTENIUM, AND SPIROTANIA. 217 
chlorophyll-bearing lichen or moss should produce a phyco- 
chrome-bearing Glcocapsa, and that, too, along with a 
chlorophyll-bearing Palmoglea. Thus, Gleocapsa polyder- 
matica surely belongs to Choococcacez, and could not be 
regarded as proceeding from a chlorophyll-bearing lichen. A 
Glceocapsa-form may possibly originate from a phycochrome- 
bearing lichen—for instance, a collema; and I venture to 
think that in many cases where Dr. Hicks speaks of Pal- 
mellacez he means to refer to Chroococcacer. Many of the 
forms included amongst the latter, I am myself disposed to 
think, show a considerable amount of instability, and may 
probably be but transitory or developmental stages of higher 
plants. But then they must, I think, at least owe their 
origin to phycochrome-containing plants—some, for instance 
may be early stages of Scytonemez. On the other hand, 
many of the forms seem to be very recognisable, and are fre- 
quently met with, season after season, precisely like their 
predecessors, and under the same circumstances ; and one 
can often at a glance tell that a certain form under observa- 
tion is exactly the same thing that one has seen before. But 
this would not in itself be an argument that they may not be, 
so to, speak, if the phrase be at all admissible, “ alternations of 
generation ” of certain Lichens or of Scytonemez. In regard 
to Palmellacez, such genera as Pleurococcus, Glceocystis, and 
Palmella, if they are all actually but developmental stages of 
higher forms, could at least originate only from chlorophyll- 
bearing plants. 
But, further, on the other hand, many of the Palmellacean 
genera produce a very definite structure, even what may be 
called a frond, and sometimes very definite forms of the indi- 
vidual cells themselves. So readily do these specialities strike 
the eye when once they have been seen, that on their recur- 
rence they are at once recognisable. The generic names 
Apiocystis, Schizochlamys, Palmodactylon, Tetraspora, Mo- 
nostroma (Ulva in part), Dictyospherium, Oocardium, 
Hormospora, Nephrocytium, Mischococcus, Ankistrodesmus 
(Rhaphidium), Polyedrium, Cystococcus, Dactylococcus, 
Characium, Ophiocytium, Scenedesmus, Pediastrum, Ccelas- 
trum, Sorastrum, Eremosphera, and many more, all call to 
mind, in a moment, forms which, some rarely, some frequently, 
present themselves to notice, and maintaining their charac- 
teristics, while at the same time no true generative process 
has been discovered, reproducing themselves by diverse modes 
of cell-division, by zoospores, by “brood-families,” &c. They 
are also found maintaining their characters in various places ; 
and I think it is not readily conceivable what yaried accidental 
VOL, VII.—NEW SER. Q 
