240 



Plant-Breeding 



closely fitted or accustomed to one set of conditions, and 

 when it is placed in new conditions, it at once makes an 

 effort to adapt itself to them. This adaptation is varia- 

 tion. No doubt the free interchange of seeds between 

 seed-merchants and customers is one of the causes of 

 the enormous increase in varieties in recent times. 



When once a novel variety appears, others of a similar 

 kind are likely soon to follow in other places, and some 



persons have supposed 

 that there is a synchro- 

 nistic variation in 

 plants, or a tendency 

 for like variations to 

 appear simultaneously 

 in widely separated lo- 

 calities. There is per- 

 haps some remote reason 

 for this opinion, because 

 there is, as Darwin ex- 

 presses it, an accumula- 

 tive effect of domestica- 

 tion or cultivation, by virtue of which plants that long 

 remain comparatively invariable may, within a short 

 time, when cultivation has been continued long enough, 

 vary widely and in many directions ; and it is to be ex- 

 pected that even when plants have long since responded 

 to the wishes of the cultivator, an equal amount or accumu- 

 lation of the force of domestication would tend to produce 

 like effects in different places. But it is probable that by 

 far the greater part of this synchronistic variation is 

 simply apparent, for whenever any marked novelty appears 



FIG. 58. Wild cabbage. 



