THE AIXLE 107 



again, for the filaments may divide up in all directions 

 into colonies of rounded cells, which may go on multi- 

 plying on their own account for some time before giving 

 rise to the ordinary form of the plant. This has been 

 called the Palmella condition, because the plant when in 

 this state has been mistaken for a distinct genus, called 

 Palmella. In other cases the cells of the filament round 

 themselves off, acquire thick walls, and may pass into 

 a resting condition. Ultimately they reproduce the 

 normal filaments, either by direct germination or by 

 forming zoospores in their interior, which escape and 

 ultimately grow into new plants. The Palmella state 

 of Ulotlirix is chiefly found when the plant is left by 

 the receding water on the damp sides of the pool or 

 stream in which it grows. The thick-walled resting- 

 cells are a means of protection against death by 

 drought. 



The great scientific interest of Ulotlirix depends on 

 the variety in its methods of propagation, and especially 

 on the fact that we can here study sexual reproduction 

 in its most primitive form. 



