30 PHYLOGENY 



assumed to have arisen. The whitlow-grasses, or Draba verna, have 

 no probable common ancestors amongst the now living forms, 

 but they are crowded together in numerous types in the southern 

 part of central Europe and more thinly spread all around, even as 

 far as western Asia. There can be little doubt that their common 

 origin is to be sought in the centre of their dominion and dispersion. 



Numerous other instances could be given, proving the occurrence 

 of smaller types within the systematic species. These subspecies 

 are of equal importance, and obviously not derived from one another 

 in a retrograde or a digressive way. They must be considered as 

 having sprung from a common ancestor by progressive steps in di- 

 verging directions. Granting this conclusion, they constitute the 

 real prototypes of progressive evolution, the actual steps by which 

 progression is slowly going on. 



Manifestly, this experience with wild plants must hold good for 

 cultivated species, too. Once these must have been wild, and in this 

 state they must have complied with the general rule. Hence we may 

 conclude that, when first remarked and appreciated by man, they 

 must already have existed of sundry elementary subspecies. And 

 we may confidently assert that some must have been rich, and others 

 poor, in such types. 



This assumption at once explains the high degree of variability of 

 so many cultivated species. This quality is not a result of cultivation, 

 but, quite on the contrary, is to be considered as originally present, 

 and one of the decisive causes, which have brought a species up to a 

 high rank in cultivation. Apples afford an instance; they are notori- 

 ous for their wide variability, but this term here only means poly- 

 morphy, indicating the existence of a large number of varieties. 

 These are found in the wild state all over Europe, differentiated by 

 various flavors and odors, but lacking the fleshiness which must be 

 added to each of the differentiating marks by an appropriate culture 

 and selection. 



Alphonse de Candolle, who has made a profound study of the origin 

 of cultivated plants, comes to the conclusion that the apple shrub 

 must have had this wide dispersion already in prehistoric times, 

 and that its cultivation must have commenced in ancient times 

 nearly everywhere. From this most important statement of so high 

 an authority we may conclude that the apples have not been taken 

 into cultivation by man in one single type, but probably in numerous 

 distinct elementary forms, transmitting thereby the wild variability 

 in a most simple and direct way to their cultivated descendants. 



It would take me too long to describe other examples. It is easily 

 seen that it is at least as probable that the notorious high variabil- 

 ity of so many of the most important cultivated plants is older than 

 their culture, as that it is to be regarded as caused by this culture. 



