8] MODIFICATION AND DISTRIBUTIONS OF CROPS 223 



categories is largely a matter of degree and hence of opinion, the 

 important feature from our point of view being that such ' poly- 

 morphs ' are able to occupy a wide range of situations and hence, 

 often, of regions. This is, however, chiefly where Man has dis- 

 turbed the native vegetation. At the other extreme we have the 

 highly specialized ' monomorphs ', such as most cultivated strains, 

 which for successful growth have to be given conditions within a 

 very narrow range of amplitude. In such circumstances they may 

 grow well enough year after year and seemingly indefinitely. But 

 once Man's influence is removed and the coarser local indigenes 

 are allowed to return to the area which is their normal heritage, 

 such pampered cultivates will disappear with surprising rapidity and 

 even aggressive weeds will usually fail within a very few years. Thus 

 in the famous Broadbalk Wilderness of Rothamsted Experimental 

 Station in southern England, according to Sir William Ogg {in litt. 

 et inch), ' The Wheat plants on the strip . , . which was allowed 

 to run wild survived for only four years ', being by then reduced to 

 ' a few stunted plants . . . barely recognizable as cultivated Wheat '. 

 Subsequently ' a dense growth of bushes and young trees ' developed, 

 which soon ceased to include even the hardier wheat-field weeds. 



Some Herbaceous Crops and Their Areas 



Most of the important plant products on which Man's sustenance 

 depends come from field or other herbaceous crops of short duration. 

 The plants involved are usually special domesticated strains that 

 have been so highly selected and long cultivated that they are unable 

 to compete with natural vegetation — perhaps anywhere in the world 

 — but, with Man's aid, they fortunately flourish sufficiently to enable 

 him to maintain his position of supremacy. Human civilizations 

 have largely developed in relation to the availability of suitable crops, 

 in particular cereals, and there is altogether widespread inter- 

 dependence between crops and Man. Communities living outside 

 the cereal belts are often backward to this day. 



W^hereas each of the various crops commonly had a single region 

 of origin — as indicated, for example, in the works of DeCandolle 

 and Vavilov cited at the end of this chapter — the main ones have 

 usually become important through having their areas spread by Man 

 into other regions. It has even been said that ' no world crop 

 originated in the area of its modern commercial importance '. Not 

 only are these regions, the present-day areas of particular crop 



