138 



MORPHOLOGY. 



nects with an empty cell of a thread which lies near as shown in 



fig. 129. If we search through the material we may see other threads 



connected in this ladder fashion, in which 



the contents of the cells are in various stages 



of collnpse 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 it forms a mass near the 



center of the cell, and again in others we 



will see that the contents 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. 



289. 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 

 conjugation are zygotes, or zygospores. 

 When we are examining living ma- 

 terial of spirogyra in this stage it is ^ ' 

 possible to watch this process of con- 

 jugation. Fig. 130 represents the differ- 

 ent stages of conjugation of spirogyra. 



290. 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 con- 

 tents of the two. tubes dissolve so that there is an open communi- 

 cation between the two cells. . The content of each one of these 

 cells which take part in the conjugation is a gamete. The one 

 which passes through the tube to the receiving cell is the supply- 



Fig. 1 29. 

 Zygospores of spirogyra. 



