GENERAL OBSEEVATIONS AND CONCLUSIONS. 461 



less similar forms, among which subordinate groups may 

 often be distinguished (races, varieties, sub-varieties), it 

 may have happened that two or more of these slightly 

 differing forms may have been introduced into cultiva- 

 tion. This must have been the case especially when the 

 habitation of a species is extensive, and yet more when 

 it is disjunctive. The first case is probably that of the 

 cabbage {Brassica), of flax, bird-cherry {Prunus avium), 

 the common pear, etc. The second is probably that of 

 the gourd, the melon, and trefoU haricot, which existed 

 previous to cultivation both in India and Africa. 



6. No distinctive character is known between a 

 naturalized plant which arose several generations back 

 from a cultivated plant, and a wild plant sprung from 

 plants which have always been wild. In any case, in the 

 transition from cultivated plant to wild plant, the par- 

 ticular features which are propagated by grafting are not 

 preserved by seedlings. For instance, the olive tree which 

 has became wild is the oleaster, the pear bears smaller 

 fruits, the Spanish chestnut yields a common fruit. For 

 the rest, the forms naturalized from cultivated species 

 have not yet been sufficiently observed from generation 

 to generation,. M. Sagot has done this for the vine. 

 It would be interesting to compare in the same manner 

 with their cultivated forms Citrus, Persica, and the 

 cardoon, naturalized in America, far from their original 

 home, as also the Agave and the prickly pear, wild in 

 America, with their naturalized varieties in the old world. 

 We should know exactly what persists after a temporary 

 state of cultivation. 



7. A species may have had, previous to cultivation, a 

 restricted habitation, and subsequently occupy an im- 

 mense area as a cultivated and sometimes a naturalized 

 plant. 



8. In the history of cultivated plants, I have noticed 

 no trace of communication between the peoples of the old 

 and new worlds before the discovery of America by 

 Columbus. The Scandinavians, who had pushed their 

 excursions as far as the north of the United States, and 

 the Basques of the Middle Ages, who followed whales 



