MISCELLANEOUS PLANTS 287 



the discovery of America. It was unknown to both the Romans 

 and the Arabs, and was not introduced into Egypt until about 

 a hundred years ago. On the other hand, Chinese literature 

 mentions the cultivation of this plant as early as the second or 

 third century, all of which is argument for an Asiatic origin. 



In the opinion of the writer these are ample grounds for 

 assuming a double origin of this most useful plant. The simi- 

 larity between the flora of eastern Asia and certain portions of 

 America is one of the best known facts in natural history. So 

 valuable a plant as the sweet potato would attract attention any- 

 where, for all the preparation needed is roasting. Accordingly it 

 would at once be brought into cultivation by any progressive race, 

 and there is every reason why widely diffused species of this kind 

 should be domesticated not once but many times, and their culti- 

 vation spread not from one but from many centers. I am of the 

 opinion that it is both unnecessary and unscientific to assume a 

 single origin for every cultivated plant. Species like the oaks, 

 growing widely scattered over the earth without the aid of man, 

 are proof of the wide diffusion of certain races by wholly natural 

 causes. Given now this same wide diffusion with evident natural 

 value to man, and we have all the conditions necessary for do- 

 mestication and cultivation, not once merely, but wherever they 

 and the needs of man come together. A good example of all 

 this in modern days is ginseng, which is native in Arabia, 

 China, and the United States. The Chinese prize this plant for 

 its medicinal properties, and as their supply is short, we are not 

 only hunting it out of the wild in the eastern hills of our own 

 country, but are beginning to cultivate it for export. 



Miscellaneous tubers. True tubers are not plentiful. The 

 onion is not a tuber, being the thickened base of the upright 

 stem. Beets and carrots are not tubers, being the true top or 

 main root greatly enlarged. Peanuts are not tubers but true 

 seeds, this plant having the curious habit of thrusting its blos- 

 soms, after fertilization, into the earth to mature and ripen the 

 seed under ground. 



