286 DOMESTICATED ANIMALS AND PLANTS 
related species is found as far north as Colorado, — the Solanum 
rostratum.+ 
At the discovery of America the potato was cultivated all 
along the Andean slopes and plateaus as far north as Granada, 
It was introduced into Europe by the Spaniards, and very likely 
from them it made its way to the United States, as it seems 
not to have been known to the Indians until after the discovery 
of this country by Europeans.? 
This tuber is one of the cheapest and most important foods 
for man, and it has done more, perhaps, than any other plant to 
make famine in the western world practically impossible. It 
made little headway, however, until recent years, for as late as 
the time of the American Revolution but two varieties were 
known in England, a white and a red. Latterly, however, great 
improvements have been made, largely within the lifetime of 
men yet living. Varieties are now counted by the hundreds, and 
any number of new ones can be produced at will, so freely does 
the species vary. 
The sweet potato (Ipomoea batatas). This is not a true potato 
at all, but belongs to the morning-glory family, whereas the 
potato belongs to the nightshades ; moreover, the fleshy parts 
that are eaten are true roots, and not thickened underground 
stems or tubers like those of the true potato. 
The origin of the sweet potato is mysterious. It was un- 
doubtedly found in cultivation in the New World. Moreover, of 
the fifteen nearest related species, all are found wild in America, 
eleven of these are found only there, while four are found also in 
the Old World. It was certainly not known in Europe until after 
1 This native sand bur was the original food plant of the Colorado potato 
beetle, but when the potato reached that region the insect at once adopted it 
as a new host, and it spread rapidly eastward over all the United States, 
illustrating how quickly a wildling may change its habits and greatly profit by 
a new food plant. 
2 Sir Walter Raleigh is often credited with having introduced both tobacco 
and potatoes into England, having brought them from Virginia, but this does 
not mean that the potato was native there, nor that this was the first introduc- 
tion into Europe. 
