DEVELOPMENT OF PLANTS 167 



other (Fig. 107, A). These tubes finally meet, when the walls 

 at the point of contact are absorbed, forming an open passage 

 between the two cells. While this growth has been going on, 



Fig. 107. Sexual reproduction of Spirogyra: A, in lower portion of 



figure the formation of the tubes between the opposite cells of the fila- 

 ments is shown. Above the contents of two cells has united with two 

 cells of another filament, forming two gametospores. B, germination of 

 a gametospore. 



the contents of the two cells has contracted somewhat and finally 

 the contents of one cell passes through the tube and fuses with 

 the contents of the other cell. In other genera, there is a con- 

 siderable modification in the process, as in some species of Zyg- 

 ncnia, where the fusion is effected in the middle of the tube. This 



