240 



GENERAL MORPHOLOGY OF PLANTS 



reproduces a new one in place of the lost half. They conjugate 

 by the protoplasts (the cell content) from two cells separating 

 from the cell wall and uniting to form a zygospore which is thick- 

 walled and often beautifully sculptured. 



SINGLE-CELLED GREEN ALG^ (PROTOCOCCOIDE^). 



373. 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. 



Fig. 183. 



Haematpcoccus lacustris = Sphaerella lacustris (Girod.) Wittrqck. A, mature free-swim- 

 ming 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 becoming green. (After Hazen.) 



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

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

 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 



* Pleurococcus vulgaris=Protococcus vulgaris. 



