158 STRUCTURAL BOTANY 



such as CEdogonium, though we can perhaps trace some 

 indication of the process in a rudimentary form. 



It has been well pointed out that the great develop- 

 ment of the sporophytic generation in the higher 

 Cryptogams may be viewed as an adaptation to life on 

 land. The sexual plant, owing to its mode of fertilisa- 

 tion, is always dependent on the presence of water ; the 

 formation of spores suitable for dissemination through 

 the air is advantageously handed over to a distinct 

 generation. In the purely aquatic Algae there is no 

 need for this double adaptation, and so we do not find 

 among them any evident distinction between a sexual 

 and a spore-bearing generation. The asexual reproduction 

 by locomotive spores is evidently adapted to aquatic life, 

 and is extremely common among Alga3 and some of their 

 nearer allies. 



As regards the mode of fertilisation, we still find in 

 CEdogonium (which in this respect is one of the highest 

 Algae) a sharp differentiation of the sexual cells on the 

 one hand the large stationary ovum, on the other the 

 small active spermatozoid. The spermatozoid, however, 

 is here much more like an ordinary cell, i.e. less specially 

 adapted for its function, than in the higher Cryptogams. 

 At the same time the unmistakable resemblance between 

 a spermatozoid and an asexual zoospore is very striking ; 

 we shall see the significance of this resemblance when 

 we come to our next type. 



It is particularly interesting that in CEdogonium we 

 have in the androspores of some species a form of cell 

 exactly intermediate between the ordinary zoospores and 

 the spermatozoids. This formation of androspores giving 

 rise to dwarf-males is quite a peculiar case, and only 

 occurs in some species of CEdogonium and in the allied 



