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NATURE OF THE KELPS 



cated by the larger size of the female cell and it is noticeable 

 that there is a decided tendency for the smaller gametes to fuse 

 with the larger and more slowly moving females. It is also 

 worthy of note that these gametes are less able to grow into weak 

 plants than in the case of the similar gametes. Thus, in Ecto- 

 carpus, we have a most remarkable series of variations that in- 

 dicate how sexuality has arisen from the asexual condition and 

 also how sex finally became characterized by a shorter motile 

 period in the female gamete. The character of the female 

 finally became more pronounced, owing to its better nourish- 

 ment and consequent increase in size and slower movements. 

 A more perfect illustration of the evolution of sex is not found 

 in nature. 



The differentiation of reproductive parts, as will be frequently 

 noted, does not keep pace necessarily with the evolution of the 

 plant body. It is evident that sexuality has arisen independently 

 at different levels in the plant world and in groups in no wise 

 connected. We have noted the same state of sexuality in some 

 of the motile green algae, i. e., in Hydrodyction and UlothrLv, 

 and now again in Ectocarpus although these plants are widely 

 separated as far as relationship is concerned and exhibit a marked 

 variation in the development of the plant body. It is also fre- 

 quently to be noted that plants may get along very well indeed 

 with only a sexual or an asexual method of reproduction. 



FIG. 120. Three of the larger brown algae: A, Laminaria. B, Lessonia. 



C, Macrocystis. 



