18 
BULLETIN 468, U. S. DEPARTMENT OF AGRICULTURE. 
of the sweeter and more juicy kinds quite generally preferred in the 
South, as distinguished from the dry, starchy varieties which are 
preferred in northern markets. 
The edible portion of the sweet potato is not a tuber like the white 
potato, but a true root. Its internal structure is more uniform than 
that of the white-potato tuber, but its role in the life history of the 
plant is much the same, that is, to act as a storehouse of plant food 
for the growth and early development of a new crop of plants. 
Above ground the plant is a vine which occasionally produces flowers 
(and in warm countries seeds) resembling somewhat those of its 
relatives, the morning-glories. The first touch of frost is fatal to the 
vines of most varieties, so the cultivation is limited to warm countries 
where the plants are perennials and the growth is practically con- 
tinuous, or to regions where the summer is long enough to insure the 
ripening of a crop. Some of the earlier maturing sorts are exten- 
sively grown as far north as Xew Jersey. 
The color of the sweet-potato skin ranges from light tan to dark 
brown, or red and purplish tones, and the flesh from almost white 
or pale lemon yellow to a deep reddish orange. The medium and 
lighter shades are most frequently seen in the northern markets. The 
weight of the roots also varies considerably, but those which are of 
medium size and of regular shape are to be preferred for the table. 
Although the bulk of the sweet-potato crop is used for human food, 
some of the coarser kinds are fed to stock, and a small part is used 
for the manufacture of starch. 
COMPOSITION AND NUTRITIVE VALUE. 
In general chemical composition the sweet-potato root resembles 
the tuber of the white potato, although there are important differ- 
ences between them. The average composition of sweet potatoes 
raw and cooked is given in Table II. together with similar figures 
for the white potato. 
Table II. — Average composition of sweet and white potatoes. 
Kind of potato. 
Sweet potato (edible portion) 
Sweet potato fas purchased) 
Sweet potato (cooked) 
Sweet potato (canned) 
White potato for comparison (edi- 
ble portion) 
Whit: potato for comparison (as 
purchased) 
Ref- 
use. 
Per ct. 
20.0 
20.0 
Water. 
Per ct. 
69.0 
55.2 
51.9 
55.2 
78.3 
62.6 
Pro- 
tein. 
Per ct. 
L8 
1.4 
3.0 
1.9 
2.2 
1.8 
Fat. 
Per ct. 
0.7 
2.1 
.4 
Carboh 
rdrates. 
Ash. 
Suear, 
starch, 
etc. 
Crude 
liber. 
Per ct. 
26.1 
21 
\2 
40.6 
Per ct. 
1.3 
.9 
.1 
.8 
Perct. 
1.] 
.9 
.9 
1.1 
18.0 | .4 
1.0 
14 
. 7 
.8 
Fuel 
value per 
pound. 
Calories. 
560 
4.50 
905 
375 
305 
