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 different 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 very noticeable, and may af- 
