THE ALG^E 167 



plantlet, which is destined to produce asexual spores, 

 but which never itself becomes a normal plant. In fact, 

 simple as Ulothrix is, it recalls to our minds, even more 

 than CEdogonium, the life-history of the higher Cryptogams. 

 The result of fertilisation is a dwarf form of plant, 

 limited almost entirely to reproductive functions, which 

 may be regarded as an extremely rudimentary sporophyte 

 generation. 



Occasionally Ulothrix reproduces itself in another way 

 again, for the filaments may divide up in all directions 

 into colonies of rounded cells, which go on multiplying 

 on their own account for an indefinite 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 Ulothrix 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 special scientific interest of Ulothrix depends on 

 the fact that in it we see sexual reproduction in its very 

 earliest beginnings, and at the same time find at least a 

 slight indication of a definite alternation of generations, 

 suggesting that of the higher Cryptogams, 



