No. IO.] FRESH-WATER ALGvE. 39 



tions, so at times a cubical colony is seen, which easily divides 

 into its respective cells. The plants are occasionally creeping, 

 branched filaments. A single parietal chloroplast is present, 

 with or without a pyrenoid. Reproduction by aplanospores 

 i. e., without cilia, by rejuvenescence of the mother-cell con- 

 tents, by isogamous gametes, or by biciliated zoogonidia. 



P. vulgaris Menegh., Fig. 73, is a very common form in 

 the state, growing in damp places, upon stones, etc. We have 

 not found it in water. 



FAMILY V. CHARACIACE^. 



Plants unicellular, usually elongated and attenuated at both 

 ends, the lower end terminating in a stalk, generally furnished 

 with a disk by which it is attached to larger Algse. A single 

 parietal chloroplast with one pyrenoid is present. Reproduc- 

 tion by numerous zoogonidia formed by division of the cell 

 contents at first transversely, then longitudinally. These por- 

 tions become rounded off, become biciliated, and escape by 

 a lateral, or, more rarely, a terminal pore. Each zoogonidium 

 becomes a new plant on coming to rest. 



Characium A. Br. Coextensive with the family. 

 C. Nagelii A. Br., Fig. 53. 

 C. ambiguum Herm., Fig. 56. 



FAMILY VI. VOLVOCACE.E. 



Plants unicellular, or consisting of ccenobia with a definite 

 number of cells, always ciliated and motile. Multiplication by 

 division of the mother-cell into 2, 4, or 8 daughter-cells. Re- 

 production both by the union of isogamous planogametes and, 

 in the higher genera, by heterogamous gametes. 



The Volvocacese are sometimes found in immense quantities, 

 and frequently give an oily taste and odor to drinking water. 

 They are closely related to the Flagellata, and some of them 

 are frequently classed with the Protozoa. 



Key to Sub-families. 



Composed of colonies of many cells ; cells with two 



cilia volvoce^e 



Composed of single cells with two, or rarely four, 



cilia CHLAMYDOMONADEyE 



