iv OBSERVATIONS ON CEREALS 95 



than other grain of the same kind which has been cultivated 

 uninterruptedly in the plains. 



2. The same thing occurs when species of cereals are 

 gradually transplanted from south to north, even when the 

 warmth is less and the sky more cloudy than in the native 

 region. 



3. The seeds of various plants increase up to a certain 

 degree in size and weight when the plants are transplanted to 

 the north, provided that they have attained their full develop- 

 ment. But they return to their original size when the plants 

 are again grown on their native southern soil. Similar relations 

 hold for the leaves of several trees and other plants. 



4. Seeds which have ripened in northern regions produce 

 larger and more vigorous plants, able to endure severe 

 weather better than those of the same species or forms which 

 are reared from seeds brought from southern districts. 



5. The formation of pigment in flowers, leaves, and seeds 

 is greater (at least up to a certain degree) in the same 

 species and varieties in northern than in southern lati- 

 tudes. 



6. In plants in which certain organs are aromatic this 

 property increases as we go northward, provided that the 

 plants attain their full development, while the proportion of 

 sugar up to a certain degree decreases. 



From these facts, of which 3 and 4 are probably to be 

 explained by natural selection, it follows amongst other things 

 that my view, namely, that an organism is altered by the 

 continued action of definite external conditions, is fully 

 justified ; for the longer it is exposed to this action the less 

 will be its tendency to reversion. Thus also the Egyptian 

 varieties of wheat are certainly not exactly the same as they 

 were 4000 years ago, even although the change is not 

 expressed in their external form but only in their constitu- 

 tion and their powers of life. For it is a proposition of special 



