164 FIELD, FOREST AND FARM 



"With some plants, let us note in conclusion, the 

 improvement attained by cultivation is more stable 

 and persists even when the seed is used for purposes 

 of propagation; but this persistence is only on the 

 express condition that our vigilance shall not relax. 

 All plants, if left to themselves and propagated by 

 seed, revert to the primitive state after a certain 

 number of generations in which the characteristics 

 imposed by human skill and care gradually dis- 

 appear." 



