166 STRUCTURAL BOTANY 



the zoospores of that plant. Now in Ulotlirix it is not 

 a mere matter of similar appearance ; the sexual cells 

 are capable of behaving like zoospores, for if conjugation 

 be not effected they can germinate on their own account. 

 It is said that in this case they always pass through 

 a resting stage, like the sexually produced zygospores. 

 Germination occurs either within the mother-cell, if they 

 fail to free themselves, or in the open, if no opportunity 

 for conjugation has arisen. We see, then, this important 

 fact : the conjugating cells have not yet become ex- 

 clusively adapted to a sexual function ; they are still 

 spores, capable of more or less successful independent 

 germination, though fitted under favourable conditions 

 for conjugation. This makes Ulotlirix and other 

 Algte like it of quite special interest, for in them 

 we can trace the very first rise of the sexual process 

 among cells which are still, to all intents and pur- 

 poses, spores. 



Conjugating motile cells are often called planogametce 

 (which implies that they are wandering sexual cells), 

 but we have not used that word so far, because it is 

 important to bring home to our minds the really funda- 

 mental fact, that the cells which conjugate are themselves 

 spores. 



Ulotlirix t though so simple an organism, has been 

 considered as presenting certain analogies with the life- 

 history of the higher Cryptogams. The resting-cell, 

 resulting from the act of conjugation, may be regarded 

 as a dwarf form of plant, limited entirely to reproductive 

 functions, and as thus representing, in an extremely 

 rudimentary form, the sporophytic generation of the 

 Bryophytes. 



Occasionally Ulotlirix reproduces itself in another way 



