220 



GENERAL MORPHOLOGY OF PLANTS 



SINGLE-CELLED GREEN ALG^ (PROTOCOCCOIDEyE). 



360. Pleurococcus.* This plant is a representative of the 

 single-celled green algae. It is often found growing on the north 

 or shaded side of trees, rocks, walls, etc., forming a thin green 

 layer. The green mass is made up of numerous green cells, 

 single or in groups of two, three, or four. These groups are 

 formed by the division of the single cells, the new cells, or 

 " daughter " cells, remaining attached for a time before separat- 

 ing. Sexual reproduction is not known. 



361. The red snow plant, Haematococcus. This is a single- 

 celled plant which, in certain stages of development, contains a 



Fig. 174. 



Sphaerella lacustris (Girod.) Wittrock. A, mature free-swimming individual with central 

 red spot. B, division of mother individual to form two. C, division of a red one to form four. 

 D, division into eight. E, a typical resting cell, red. F, same beginning to divide. G, one 

 of four daughter zoospores after swimming around for a time losing its red color and be- 

 coming green. (After Hazen.) 



red pigment which disguises the color of the chloroplast. It is 

 often found covering large tracts of snow in arctic regions. A 

 very closely related species, if not the same, inhabits the shores 

 of lakes, ponds, and streams in rocky areas of the North Tem- 

 perate region. It is often found in shallow depressions of rock 

 along the shore, where in dry weather it resembles a coat of dull 

 red paint on the rocks. The plant is now in the resting stage. 

 When rains come the plants revive, come out of the resting state, 

 are provided with two long lashes or whips (cilia or flagella) 

 * Pleurococcus vulgaris = Protococcus vulgaris. 



