126 VARIOUS FOOD-PLANTS 



48. The multiplication of varieties. Besides the effect 

 which geographical range has exerted upon the spread and 

 period of cultivation, the differences in the number of varie- 

 ties that have arisen through human agency among culti- 

 vated plants may be attributed largely to the same important 

 factor; since, as may be readily shown, the number of varie- 

 ties in a given species is much influenced by the extent and 

 duration of its culture. For, taken as a whole, the plants of 

 ancient or prehistoric cultivation, as compared with those of 

 modern or recent introduction, present a marked contrast 

 in the greater number of clifTerent varieties which have come 

 to be cultivated. Thus we have the common buckwheat, 

 a "modern" plant, without any well-marked varieties, as 

 against the "ancient" oats and rye, each with several varie- 

 ties; and the "prehistoric" wheat, barley, rice, and maize, 

 with scores or hundreds of varieties. If the comparison of 

 the newer with the older be extended to nuts, vegetables, 

 and fruits, a similar rule will be found to obtain; although it 

 is true that more or less important exceptions will be encoun- 

 tered. These exceptions go to show that other elements 

 besides time of culture would have to be taken into account 

 in any attempt to explain fully why one cultivated species 

 should have more or less varieties than another. But these 

 other factors need not be here considered, since our present 

 purpose is to point out that just as the area of use and the 

 culture-period of a plant have been dependent largely upon 

 the geographical relation of its native home to a primitive 

 center of agriculture, so upon these factors, in their turn, 

 have largely depended the number of varieties which have 

 been artifically developed. 



49. How varieties arise. Finally, a brief consideration of 

 how such "artificial" varieties arise, will help us to under- 

 stand why it is that long and widespread cultivation should 

 tend to increase the number of these varieties. It will be 

 remembered that when discussing what is meant by a "va- 

 riety" as distinguished from a "species" (section 9) the state- 

 ment was made that no two individual plants are exactly 

 alike even though raised from seeds of the same parent. 

 Sometimes the differences are verj'- noticeable, and may af- 



