274 NATUEAL HISTORY SOCIETY OF DUBLIN. 



Monostroma (Ulva in part), Dictyosphaerium, Oocardiuin, Hormospora, 

 E"ephrocytium, Mischococcus, Ankistrodesmus (lihaphidium), Polye- 

 drium, Cystococcus, Dactylococcus, Characium, Ophiocytium, Scenedes- 

 mus, Pediastrum, Ccelastrum, Sorastrum,Eremospba3ra, and many more, 

 all call to mind, in a moment, forms which, some rarely, some frequently, 

 present themselves to notice, and maintaining their characteristics, 

 while at the same time no true generative process has heen discovered, 

 reproducing themselves hy 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 varied accidental concatenation of circumstances could, in so di- 

 verse localities, force a certain supposed gonidium of a lichen or spore 

 of a moss now to develope into this well-defined form, now into that. 

 Therefore, if, on the one hand, such genera perhaps as Chroococcus, 

 Glceocapsa, Synechococcus, Glceothece (in Chroococcacese) and Pleuro- 

 coccus, Glceocystis and Palmella (in Palmellaeese), seem, from Dr. 

 Hicks' s researches, to be in jeopardy, it surely appears to me as yet, 

 not to speak of cur Cylindrocystis, Mesotsenium, and Spirotaenia, that it 

 would be an incautious and too hasty conclusion to sweep away all 

 " Paluiellaceae." 



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 doubt varies within certain, often charac- 

 teristic, limits. 



Position of nucleus? or of a starch granule or a "vesicle" ? The 

 former is seldom 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, Con- 

 jugatse at large, &c. &c. Dr. Hicks, indeed, supposes the case of 

 " Zygnema" (properly Spirogyra), in which the contents in conjugat- 

 ing lose their spiral arrangement, 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, producing thus 

 the "root- cell," 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. There is, indeed, more of a characteristic uni- 

 formity in the disposition of the phy cochrome in the Chroococcaceae. 



Form of the cell ? This is surely in many instances of the greatest 

 value. Dr. Hicks points to the Plate illustrating my own former 



