CHAPTER III 

 FOOD MANUFACTURE 



22. Peculiar work of green plants. The Algae differ from 

 other Thallophytes in containing chlorophyll ( 10, p. 10). 

 The presence of this pigment is so common among plants 

 that vegetation is thought of as being green, but very many 

 plants are not green. Even those that contain chlorophyll 

 are not always green in appearance, for this pigment may be 

 obscured by others. For example, there are four groups 

 of Algae that are distinguished by their color, although all of 

 them contain chlorophyll. The two conspicuous groups of 

 fresh-water Algae are called " Blue-green Algae " (Cyano- 

 phycece) and "Green Algae" (Chlorophycece) because in the 

 former a blue pigment is associated with the green, giving 

 the plant a bluish green tint, and, in the latter, chlorophyll 

 is the only pigment. The two conspicuous groups of marine 

 Algae are called " Brown Algae " (Phceophycece) and " Red 

 Algae " (Rhodophycece) because in the former certain brown 

 and yellow pigments are associated with the green and often 

 mask it completely, and in the latter a red pigment obscures 

 the green. 



The presence of chlorophyll in the Algae gives them a 

 peculiar power among Thallophytes, a power that all green 

 plants possess. It is the power of manufacturing food. 

 It is perhaps impossible to define exactly what is meant by 

 food, but in general it means material that protoplasm can 

 use in building up its body. All living things must use food, 

 but only green plants can make it. This process, therefore, 

 is one of the very greatest importance, for the existence of 

 all plants and animals depends upon it. 



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