LIFE HISTORIES OF ALG^ 



253 



of a tiny green plant, called Pleurococcus, usually of the 

 species Pleurococcus vulgaris. The individual plants are 

 so small that they may be seen only with the aid of the 

 microscope (Fig. 183). An examination of the trees in 

 any given locality will disclose the fact that Pleurococcus 

 prefers one side of the tree to the other, and that the 

 choice of sides has a direct relation to light, temperature, 

 or moisture — one or all. 



Fig. 184. — Pleurococcus vulgaris. Sections of one-, two-, and four-celled 

 plants, showing the nuclei and the large chlorophyll bodies (chb) to which 

 the green color of the plants is due. In D, the larger chloroplast is shown 

 in perspective. (Camera lucida drawings from a microscopic preparation 

 by E. W. Olive.) 



243. Structure. — No plant structure could be much 

 simpler than that of Pleurococcus, for the plant body is a 

 single cell, the simplest organic unit capable of independent 

 existence. The protoplast possesses a well-defined nucleus 

 and a chloroplast, and is surrounded by a cellulose cell- 



