2 BULLETIN 50, HAWAII EXPERIMENT STATION. 
BOTANICAL RELATIONSHIP. 
The sweet potato belongs to the morning-glory family (Convolvu- 
lacese) and is known botanically as Ipomcea batatas. It is probably 
indigenous to the West Indies or Central America. In the Tropics 
this plant is a perennial and produces long trailing stems. Except 
in case of a few varieties, the sweet potato blooms profusely in 
Hawaii from November to April. The shape of the leaves and the 
color of the skin and flesh differ with the variety. The skin ranges 
from white to dark brown in color, and the flesh varies from white 
to pumpkin and dark purple. 
CULTIVATION IN ANCIENT TIMES. 
The sweet potato was grown with care by the ancient Hawaiians. 
The vines for planting were not gathered at random, but with a 
discrimination which showed that the native agriculturists ap- 
preciated the importance of selection. Vines of individual plants 
bearing roots in large quantities were selected for further planting. 
PLACE IN THE HAWAIIAN CROPPING SYSTEM. 
From ancient times the native Hawaiian farmer has realized the 
advisability of alternating his sweet potatoes with other cultivated 
crops to improve the physical condition of the soil. Observation 
taught him that land which was allowed to rest for a year or so after 
having produced a sweet-potato crop yielded a better and heavier 
crop than did ground which was kept continuously in one crop. 
Weeds and native grasses were therefore allowed to grow for a reason- 
able length of time before the land was replanted to sweet potatoes. 
The rice planters of to-day use the sweet potato and other cultivated 
crops in their system of rotation. As soon as the last annual grain 
crop has been harvested, the coarse straw is burned and the stubble 
is turned under and harrowed. The land is then given a heavy appli- 
cation of manure and is immediately used for some quick-growing 
vegetable, such as lettuce, spinach, beets, radish, or mustard cabbage, 
followed by sweet potatoes. 
The following cropping systems are recommended for use in con- 
nection with sweet-potato cultivation in Hawaii: 
Two-year rotation. — Corn, cowpeas, sweet potatoes, peanuts; or 
sweet potatoes, beans, buckwheat, cowpeas, and corn. 
Three-year rotation. — Corn, peanuts, grass or sorghums, cowpeas, 
and sweet potatoes. 
Four-year rotation. — Corn, mungo beans, sorghum, alfalfa, and 
sweet potatoes. 
Five-year rotation. — Corn, peanuts, sorghum, pigeon peas, sweet 
potatoes; or cassava, cowpeas, peanuts, sweet potatoes, and alfalfa. 
ADAPTATION TO HAWAII. 
Hawaii, being situated well within the Tropics, is naturally adapted 
to the growing of sweet potatoes. The situation is so favorable, in 
fact, that the plant produces immense roots, even when it is grown 
in the pockets of volcanic rocks where there is little soil. The sweet 
potato can be grown on all the areas of Hawaii except in rocky 
