CHAPTER V 

 THE ALG^E 

 Thallophytes 



ALL plants below the Mosses are often placed in a single sub- 

 kingdom, Thallophyta, but there are good reasons for considering 

 the two great divisions above the Schizophytes and below the Mosses, 

 as entitled to the rank of subkingdoms. Those forms which possess 

 chromatophores are known as Algae; those from which they are 

 absent, Fungi. The Schizophytes are often included with the Algae, 

 but they, as well as the Myxomycetes and Flagellata, which are 

 sometimes united with the lower Algae under the name Protophyta, 

 are probably also better regarded as subkingdoms. 



The Algae 



The Peridinese and Diatomaceae, both of which groups are related 

 more or less closely to the higher Algae, may probably best be con- 

 sidered as the two lowest classes of the subkingdom. Leaving 

 these aside, the Algae are usually divided into three classes, the 

 Green Algae (Chlorophyceae), the Brown Algae (Phseophyceae), and 

 the Red Algae (Rhodophyceae). The supplementary pigments which 

 distinguish the two latter classes from the Chlorophyceae are associ- 

 ated with marked structural differences which sharply separate the 

 three classes. One group of the Green Algae, the Characeae, may 

 perhaps be better removed from that group and considered as a 

 fourth class. 



CLASS I. THE GREEX ALG^E (CHLOROPHYCEAE) 



The Green Algae are especially interesting because, with little 

 question, they represent more nearly than any other existing plants 

 the ancestors of the green land-plants. The Phaeophyceae and Rho- 

 dophyceae, on the other hand, are to be regarded as much more 

 specialized forms, especially adapted to a marine environment, and 

 as having diverged widely from the forms which have given rise 

 to the higher green plants. 



Chromatophores. The Chlorophyceae always contain distinct chro- 

 matophores, which seldom show any other color than pure green, 



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