70 Plant Life and Evolution 



red algae, are forms which have become most 

 perfectly adapted to strictly marine life, most of 

 the more primitive green algae being confined to 

 fresh water. Of the two classes of seaweeds the 

 brown algae probably constitute a separate line, de- 

 rived from some flagellate ancestors. The red 

 algae, while different in many ways from the green 

 algae, still among their lower members show points 

 of resemblance which do not forbid the hypothesis 

 that they may have arisen from forms allied to some 

 of the green algae. This view is strengthened by 

 the fact that a good many of the more primitive 

 types of the red algae inhabit fresh water. The 

 true brown algae are almost exclusively marine in 

 habit. 



If, as has been conjectured, the ancient seas were 

 much less saline than those of the present time, it 

 may be that the green algae as they now exist are 

 the little changed descendants of the primordial 

 algal types which have persisted in fresh water 

 and retained most of their original characteristics. 

 The brown algae, so far as we can judge, are essen- 

 tially marine, and both color and structure may be 

 considered to be direct adaptations to the marine 

 life. The brown pigment is assumed to be pro- 

 tective, as these plants are often exposed to strong 

 light when uncovered by the tides, and the leathery 

 texture and gelatinous tissues of the larger forms 

 are evidently associated with their growth on ex- 

 posed rocky shores. 



