SPIROGYRA. 117 



we search through the material we may see other threads con- 

 nected in this ladder fashion, in which the contents of the cells 

 are in various stages of collapse from what we have seen in the 

 growing cell. In some the protoplasm and chlorophyll band 

 have moved but little from the wall ; in others they form a mass 

 near the centre of the cell, and again in others we will see that 

 the content of the cell of one of the threads has moved partly 

 through the tube into the cell of the thread with which it is 

 connected. 



This suggests to us that the oval bodies found in the cells 

 of one thread of the ladder, while the cells of the other thread 

 were empty, are formed by the union of the contents of the 

 two cells. In fact that is what does take place. This kind 

 of union of the contents of two similar or nearly similar cells is 

 conjugation. The oval bodies which are the result of this con- 

 jugation are zygotes, or zygospores. When we are examining 

 living material of spirogyra in this stage it is possible to watch 

 this process of conjugation. Fig. 94 represents the different 

 stages of conjugation of spirogyra. 



202. How the threads conjugate, or join. — The cells of two 

 threads lying parallel put out short processes. The tubes from 

 two opposite cells meet and join. The walls separating the 

 contents of the two tubes dissolve so that there is an open 

 communication between the two cells. Each one of these cells 

 corresponds to a sexual organ. This process of conjugation is 

 a sexual process. The process here is a very simple one be- 

 cause any cell of the thread without any particular change in 

 size or form may become a sexual organ. The cell which loses 

 its protoplasm is the supplying cell, while the one in which th e 

 zygospore is formed is the receiving cell. Before the movement 

 of the protoplasm begins we cannot tell which is to be the sup- 

 plying cell or the receiving cell. 



The passage of the protoplasm from one cell to another can 

 only be seen under the most favorable conditions, and then with 

 living material. It is possible, howevei, in preserved material 



