126 ^■AKI(JUS FOOD-PLANTS 



48. The multiplication of varieties. Besides tlie effect 

 which geographical range has exerted upon the spread and 

 period of cultivation, the chlferences in the numlter of varie- 

 ties that have arisen tlirough human agency among culti- 

 vated plants maj' be attri))uted largely to the same important 

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

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

 duration of its culture. For, tafcen 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 different varieties ^vhicli 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 he 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 fullj' why one cultivatetl 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 lirief considi'ratiun of 

 how such "artificial" varieties arise, will helj:) us to under- 

 stand why it is that long and widespread cultivation should 

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

 remembered that A\-hen discussing what is m(>ant Ijy a "^•a- 

 riety" as (hstinguished from a "specit>s" (section 9) the state- 

 ment was made that no two individual plants are exactly 

 alike even th(jugh raised from seeds of the same parent. 

 Sometimes the differences are very noticeable, and may af- 



