CHAPTEE III 



THE ALG^E 



THE Sub-kingdom with which we have now to make 

 ourselves acquainted differs profoundly from any of 

 those of which representatives have been already con- 

 sidered. In habit all the plants included under the 

 general heading " Algae " are totally different from any 

 hitherto described, and at the same time they differ more 

 among themselves than the lowest Liverwort differs from 

 the most complex Dicotyledon. The members of the 

 group most familiar to ordinary readers are the Seaweeds, 

 for with very few exceptions all plants which grow in 

 the sea belong to the Algae. On the other hand, an 

 immense number of species are inhabitants of fresh water, 

 or can get on, like the American steamboat, " wherever 

 it is a little damp." Generally speaking, the larger and 

 more complex forms are marine ; . the fresh-water and 

 terrestrial representatives are both smaller and simpler. 

 Among Seaweeds there are species which rank with the 

 most gigantic members of the Vegetable Kingdom, while 

 there are other Algae which are entirely invisible as 

 individuals to the naked eye. The higher Algae often 

 show a complex external form, with organs analogous to 

 the root, stem, and leaf of the higher plants ; at the 

 same time, their tissues are highly differentiated. On 



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