1 5 6 



LIFE HISTORY OF SPHAERELLA 



divisions, the red coloring matter is usually rapidly replaced by 

 chlorophyll until but a red speck remains and the zoospores soon 

 appear as rather ovate green cells surrounded by delicate walls 

 which become widely separated from the chlorophyll owing to 

 the accumulation of water (Fig. 100, G). Nearly all zoospores 



FIG. 100. Stages in the life history of Sphaerella: A, resting state of 

 the plant. B, first division. C , second division, the four cells are about 

 to escape from the mother plant. D, one of the cells of C after escaping. 

 This is a zoospore of the first generation. E, zoospore at rest. F, forming 

 four new zoospores. G, one of these zoospores of the second generation. 

 Note that the red material, represented by the shaded area in the center 

 of the cell, has become greatly reduced and that the wall is becoming 

 distended and separated from the granular cytoplasm. H, third resting 

 stage. /, cell dividing. K, zoospore of third generation with greatly dis- 

 tended cell wall and small red area. Delicate strands of cytoplasm connect 

 the cell wall and the central protoplasmic body. L, a resting cell dividing 

 into a large number of zoospores which are consequently smaller. After 

 Hazen. 



that occur among the algae are characterized by a small red body, 

 known as the eye spot, which is located near the ciliated end of 

 the zoospore. It has been supposed that this body is sensitive 

 to light and gives the zoospore a sense of direction. While this 



