DEVELOPMENT OF PLANTS 



165 



divisions, the red coloring matter is usualy 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 SphaereUa: 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 distended 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 



