124 PLANTS AND MAN 



grass or other vegetation. Such a run-off of the rainfall has 

 several far reaching and disastrous consequences. One is the 

 swelHng of the streams and rivers so that floods result; another 

 is the small amount of rainfall that can soak into the ground and 

 remain there as ground water, to seep into springs and thus keep 

 our reservoirs filled with pure drinking water. If, on the other 

 hand, the soil is covered with vegetation, much more of the rain- 

 fall goes into the ground, since the roots form a spongy network 

 which absorbs the water at the same time that it prevents erosion 

 of the soil. Removal of forests at the headwaters of any river 

 system usually causes periodic floods farther down the course 

 of the main river. 



Another beneficial aspect of our inter-relations with the plant 

 world is associated with the esthetic appeal of plants. Most of us 

 have a deep-seated liking for the companionship of plants; we 

 like their comforting shade, their fragrance, their colorful blos- 

 soms; we like to have trees and flowers around us, whether in 

 elaborate gardens or in window boxes and pots. Millions of dol- 

 lars are spent annually by taxpayers for plants which beautify 

 their public streets and parks. Ornamental plants help to make 

 urban living more tolerable; garden clubs flourish best, it seems, 

 in large cities. Few of us would deliberately choose to live in a 

 region in which there is no plant life at all; and the attrac- 

 tiveness of many recreational areas — whether golf clubs, fishing 

 and hunting preserves, state or national parks — depends upon 

 the character of the vegetation. Life without plants, entirely 

 apart from their dollars-and-cents value, would be much less 

 pleasant. This aspect of plant appreciation forms the subject 

 matter of Part Six of this text. 



Plant Relations Harmful to Man 



Plants are not, unfortunately, entirely beneficent in their 

 relations with animals and man. Because of their inherent 

 metabolic shortcomings, the colorless plants have always been a 

 menace to self sustaining green plants and to animals. Most 

 harmful of the colorless plants, from the human viewpoint, are 

 the microscopic bacteria which cause diseases. In size and struc- 

 ture they are insignificant organisms; yet they are one of the few 



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