80 PRACTICAL BOTANY. 



along, or simply rotates in its position without motion 

 from place to place. 



The whole colony is green in color because of the 

 presence of chlorophyl granules in the protoplasm of the 

 flagellate cells. These cells closely resemble the flagellate 

 cells of Protococcus pluvialis, and could hardly be distin- 

 guished from them were it not for the manner in which 

 they form spherical aggregations, while the cells of Pro- 

 tococcus naturally separate. 



The reproduction is by both the asexual and the sexual 

 ways. The asexual multiplication occurs in the earlier 

 part of the season. A flagellated gonidial cell divides 

 and subdivides into many parts, which escape into the 

 interior of the mother colony, where they unite to form 

 a new colony. 



The sexual multiplication occurs late in the season. 

 Some of the flagellated cells develop into sperm cells, the 

 male gametes ; others develop into germ cells, the female 

 gametes. Both germ cells and sperm cells may be pro- 

 duced by the different differentiation of the flagellated 

 cells of the same colony, or they may be formed on dif- 

 ferent plants. When the germ cells have matured, they 

 are loosened from their positions in the shell of the colony 

 and pass into the hollow interior. In the sperm cells a 

 great many antherozoids or minute cells provided with 

 flagella are developed. These are set free by the break- 

 ing down of the wall of the cell in which they are formed, 

 and, swimming about, find their way into the interior of 

 the colonies containing the germ cells, which they meet 

 and fertilize. There results a resting spore with a thick 

 cell wall. After a period of rest, the resting spore, when 

 favorable conditions exist, resumes active life. Its pro- 

 toplasm breaks up into a great many small cells which 

 assume the spherical form and grow to be a full-sized 

 colony. 



