88 FRESH-WATER ALG^ OF THE UNITED STATES. 



diameter of these hsematococcus cells to be one twelve-hundredth of an inch 



(.00083"). 



MM. Pamnitzinand Boranetzky, in a recent paper ("Zur Entwickelungsgeschichte 

 der Gonidien und Zoosporenbildung der Flechten," Mem. de L'Academie Imperiale 

 des Sciences de St. Petersbourg, 1868, Annals and Mag. Nat. History, Feb. 1869), 

 state as the result of direct observation that this genus of algse, so called, is really 

 a stage in the life history of the gonidia of lichens. These gentlemen took thin 

 slices of lichen thalli containing gonidia, and placed them upon pieces of iir and 

 .linden bark, which had been previously boiled to kill any plants that might be 

 growing on them. These were then put in a glass jar inserted over a vessel con- 

 taining water, in such way that they would be constantly exposed to a very damp 

 atmosphere, and at the same time communication with the external air would be 

 impossible. In another set of experiments, pieces of the lichens were allowed to 

 lie for a long time in water, until the component filaments were decomposed into 

 a gelatinous mass, in which the still green vigorous gonidia were imbedded. These 

 pap-like (breiige) masses were then washed with pure water .and smeared upon 

 pieces of linden bark. The results obtained were identical -in the two cases. The 

 gonidia were at first provided each with a distinct nucleus and a well-marked 

 lateral vacuole, and resembled closely the first form of cystococcus. The next 

 change was a division of their contents into a large number of roundish masses, 

 with the disappearance both of the vacuole and of the central nucleus. The cell- 

 membranes were next ruptured, and the endochrome, protruding through the open- 

 ing, formed a little ball sitting upon the parent cell. In doing this it doubled 

 in size, so that the part without was as large as the part within, although the latter 

 stUl filled the cell. The contents finally escaped, but were yet surrounded by a 

 very thin membrane, which soon, however, ruptured, and freed the biciliated 

 zoospores into which the endochrome had in the mean time resolved itself. These 

 zoospores remained a long time in the motile state, but finally settled down, drop- 

 ping their cilia, and became little round cells, which grew to three or four times 

 their original size. Further development was not made out. 



Certain of the gonidia, belonging to a lichen of the genus Physcia, failed to 

 produce zoospores, but their endochrome, divided so as to form a number of 

 quiescent cells, which either ruptured very early the original cell-membrane and 

 became free in the water, or else remained bound together by it into a family for a 

 longer period. In these researches MM. Pamnitzin and Boranetzky employed 

 lichens of three genera, namely Physcia, Cladonia, and Evennia, and claim, as 

 above stated, that their investigations prove that they developed the algge genus 

 Cystococcus of Nsegeli {Ghlorococcum, Pries), from the gonidia. 



Genus POLYEDRIUM, N^geli, (1849.) 



Cellulse singulae, segregatse, libere natantes, compressse, 3-4-8 angulares, angulis plus minus pro- 

 ductse, nonnunquam radiatim elongat83, aut integrae aut bifidse, plerumque armatfe, a latere oblongo- 

 ellipticK, utroque polo rotundatse vel subtruncatse. Cytioderma tenue, Iseve. Massa chlorophyl- 

 lacea plerumque granulosa, per cellulsa lumen sequaliter distrlbuta, nonnunquam guttulis oleosis 

 rubris 1-4 mixta. 



Propagatio adhuc iguota. (R.) Genua mihi ignoium. 



