l8] PLANT ADJUSTMENTS AND APPLICATIONS 569 



Conservation, which largely depends on wise treatment of vegeta- 

 tion, is a rapidly developing theme, of the utmost significance to 

 civilization. Prevention is far better than cure, but very often we 

 are too late for the former and sometimes even for the latter. Of 

 this we have already seen instances, a terrible one being indicated 

 in Fig. 181. In other cases remedy may be simple, as illustrated 



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Fig 



-Delstructive water-erosional gully in heavily o\'ergrazed pasture in 

 Illinois. (Courtesy of U.S. Soil Conservation Service.) 



in Figs. 182 and 183, where bad water-erosion was stopped by 

 simply excluding livestock for two years and so allowing succession 

 to proceed. In yet other cases all that is needed may be a planting 

 of Willows on a stream-bank or of Lyme-grass on the windward 

 slopes of sand-dunes. Yet altogether an appalling proportion of the 

 once-productive land areas of many major countries has been lost 

 to cultivation owing to unwise practices following Man's desecration 

 of vegetation. This has led particularly to devastating erosion, and 

 judicious planting of suitable crops or binders is often the best key 

 to the reclamation of such tracts w'here this is possible. In the 

 continental United States, for example, the area of cropland that 



