ALG^ IN GENERAL 



•491 



described in our examples of brown algae, and many of the 

 red seaweeds rival the brown in elaborate forms of thallus 

 simulating remarkably the shoots of higher plants. 



177. The seaweed subdivision, algae in general. It is 

 beheved by evolutionists that life originated in the sea. 

 Among the algae we generally find that the marine forms are 

 more primitive than their nearest relatives growing in fresh 



Fig. .321. — Carragcfo (.see also Fig. 118). A, transver.sc section through a 

 fruiting branch showing the spore-clusters embedded in the thallus, ■■"-. 

 B, same, "-i-^, showing rind (r), pith-Ul<:e interior (m), and spore-clustera 

 (s). (Luerssen.) 



water or in the air. Hence, as being at once the most primi- 

 tive and most typical of the algte, seaweeds may not inappro- 

 priately serve to name the entire group. Over 12,000 species 

 of algae are known. In spite of the great variety of form in 

 the plant-body and in the life-histories of various algae, an 

 alga may generally he recognized as a plant without true roots, 

 stems, or leaves, but containing chlorophyll, although the leaf- 

 green color may he masked hy some other -pigment. 



It must not be supposed that the pigments which have suggested 

 names for the several classes of algse are invariably present in these 

 groups, or that mere color is here the basis of classification. The 

 pigments in question happen to be associated very generallj^ with 

 fundamental peculiarities of structure and hfe-history which give 

 evidence of kinship; hence algoe of the same color may as a rule be 

 regarded as akin and thus the pigments afford a convenient though 

 superficial mark for recognizing related forms. 



