458 ORIGIN OF CULTIVATED PLANTS. 



very ancient cultivation, or four per cent., and these are 

 two species which probably exist no longer as wild plants. 

 I believed, d priori, that a great number of the 

 species cultivated for more than four thousand years 

 would have altered from their original condition to such 

 a degree that they could no longer be recognized among 

 wild plants. It appears, on the contrary, that the forms 

 anterior to cultivation have commonly remained side by 

 side with those which cultivators employed and propa- 

 gated from century to century. This may be explained 

 in two ways : 1. The period of four thousand years 

 is short compared to the duration of most of the specific 

 forms in phanerogamous plants. 2. The cultivated 

 species receive, outside of cultivated ground, continual 

 reinforcements from the seeds which man, birds, and 

 different natural agents disperse and transport in a 

 thousand ways. Naturalizations produced in this manner 

 often confound the wild plants with the cultivated ones, 

 and the more easily that they fertilize each other since 

 they belong to the same species. This fact is clearly 

 demonstrated in the case of a plant of the old world 

 cultivated in America, in gardens, and which, later, 

 becomes naturalized on a large scale in the open country 

 or the woods, like the cardoon at Buenos Ayres, and the 

 oranges in several American countries. Cultivation 

 widens areas, and supplements the deficits which the 

 natural reproduction of the species may present. There 

 are, however, a few exceptions, which are worth men- 

 tioning in a separate ai'ticle. 



Article. IV. — Cultivated Plants which are Extinct, or 

 becoming Extinct in a Wild State. 



These species to which I allude present three remark- 

 able characters : — 



1. They have not been found wild, or only once or 

 twice, and often doubtfully, although the regions whence 

 they come have been visited by several botanists. 



2. They have not the faculty of sowing themselves, 

 and propagating indefinitely outside cultivated ground 



