n] THE BEACH AND ROCKS 27 



are of prime importance as they a/ffect the outlook 

 upon the vegetation of the earth. Guided by such 

 study we shall regard the condition of simple 

 organisms motile in water as primary ; the encysted 

 state of the protoplasm and the fixed position as 

 a secondary condition acquired as a concession to 

 nutritive convenience and mechanical protection ; 

 the process of sexual fusion itself appears also to 

 be secondary, originating perhaps as a method of 

 strengthening attenuated zoospores ; while, lastly, 

 the sexes were in the first instance alike, the differen- 

 tiation of the sexes having arisen subsequently to 

 the origin of sexuality. It probably arose in relation 

 to the necessity for adequate nutrition of the germ, 

 so that after fertilisation it may make an efficient 

 start in life, and successfully perpetuate its race. 



Returning in conclusion to the Flora of the shore 

 as a whole, with its varied forms, Green, Brown, and 

 Red, they together with certain dwellers in fresh 

 water form a vegetation apart. These plants have 

 developed in accordance with their aquatic surround- 

 ings, and in their own way some of them have attained 

 a high complexity not only of form and construction, 

 but also of propagative method. But they always 

 bear the impress of their aquatic habitat, and differ 

 in essential features from the characteristic Flora 

 of the land. Their higher representatives may then 

 be regarded as being the culmination of their 



