188 GERMINATION OF THE GAMETOSPORE 



gametospore becomes surrounded by a thick wall and in this 

 resting condition it tides the plant over seasons, such as the 

 winter or drought, unfavorable for the growth of the plant. 

 When conditions return that permit the growth of the plant, 

 the gametospore germinates by rupturing the outer wall and pro- 

 truding the inner wall of the spore as a delicate tube (Fig. 107, B) . 

 Early in this germination the nucleus divides, forming four cells, 

 the outermost of which only continues to grow and so ultimately 

 forms the new plant. Note that the gametospore, therefore, 



E 



FIG. 108. Common forms of Desmids: A, Closterium. B, Micrasterias . 

 C, Xanthidium. D, Staurastrum. At left top view, at right side view. E, 

 Desmidium forming a chain of plants. At right, end view of chain. 



does not grow directly into the parent type of plant. This be- 

 havior of the gametospore is one of the most fundamental 

 features in plant life. It appears in the preceding groups but 

 it is mentioned now for the first time because we see here a clear 

 demonstration of its character. The gametospore is different 

 in its nature and possibilities of growth from any one of the cells 

 of the parent plant. It can not produce the spirogyra plant. 

 It can only produce four cells and from one of these cells there 

 will develop the spirogyra plant. Further consideration of this 

 feature in the life history of the plant will be deferred to later 



