Chapter 16 



ECONOMIC IMPORTANCE OF PLANTS 



Naturally, not all plants of economic importance or the economic 

 importance of all plants listed can be fully considered in one chapter. 

 Economic importance is considered from the beneficial as well as the 

 detrimental standpoint. Certain phases of economic biology are also 

 considered in the chapter on Applied Biology. Greater emphasis con- 

 stantly is being placed on the economic importance of both animals and 

 plants in everyday life. Consequently, a consideration of a few repre- 

 sentative phases in courses in biology is essential. The following de- 

 scriptions are representative but by no means complete. For more 

 detailed discussions the reader is referred to books on economic botany. 



I. ECONOMIC IMPORTANCE OF ALGAE (Figs. 29 to 33) 



Certain blue-green algae (phylum Cyanophyta) may become so abun- 

 dant in fresh water as to produce a distinct color, the so-called "water 

 bloom." When they die and decay, they may give the water a very 

 unpleasant taste and odor. Cattle have been known to die by drinking 

 water in which they were very abundant. The larger brown algae 

 (phylum Phaeophyta) are a source of such materials as iodine and 

 potash. The red algae (phylum Rhodophyta) are sources of agar-agar 

 which is used as a medium for the cultivation of bacteria as well as for 

 a medicine. A jellylike food is obtained from the red alga known as 

 "Irish moss." Certain types of red algae become encrusted with lime 

 and thus help in the formation of the so-called "coral" reefs, atolls, and 

 islands. 



Because of their toughness, certain algae when dried are used in mak- 

 ing fishing lines, handles for tools, and similar objects. Certain seaweeds 

 (algae) as well as diatoms (phylum Chrysophyta) are used by various 

 animals for foods. 



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