CHAPTER XXIII. 

 ALGvE. 



347. The algae are plants of a low grade of organization. 



They live in the water, or a few of them in moist situations. 

 Those growing in the sea are popularly called " sea mosses," while 

 those growing in fresh water are called " pond scums," " water 

 nets," etc. It should be understood that the algae are not true 

 mosses. They are all simpler in structure and lower in the scale of 

 classification than the mosses. The simplest algae are single-celled 

 plants. From this simple condition single individuals or cells are 

 easily associated into colonies, or firmly united into filaments, or 

 cell plates, which reach massive size in the rockweeds and kelps. 



348. The plant body of the algae thus varies greatly in size 

 as it does in form. The plant body of the algae is not divided 

 into true stems, roots, and leaves. There are, it is true, algae which 

 possess root-like, stem-like, and leaf -like organs, but they do not 

 belong to the same part in the plant's life cycle that the true roots, 

 stems, and leaves of the ferns and seed plants do. For this reason 

 they are not regarded as true roots, stems, or leaves from the 

 standpoint of comparative morphology, although from the stand- 

 point of physiology or function such algae possess stems and 

 leaves. Such a plant body, which is not differentiated into true 

 roots, shoots, and leaves, is called a thallus. The plant body of the 

 algae as well as of the fungi is a thallus. They are characteris- 

 tically the thallus plants or Thallophytes. 



The algae possess chlorophyll * and are thus able to live inde- 



* There are a few parasitic algae which lack chlorophyll, and their 

 method of nutrition is similar to that of the fungi, although some of them 

 store starch which they obtain from their green host. Example, Rhodochy- 

 ttium, parasitic on the ragweed in North Carolina, and probably other 

 Southern and Atlantic States, and on one of the milkweeds in Kansas. 



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