MISCELLANEOUS PLANTS 257 
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. 
