CULTURAL DIRECTIONS 
439 
The Porto Rico is a very popular moist-fleshed variety, 
and with the exception of the Nancy Hall is grown more 
extensively than any other variety in the South. The 
vines are long growing and coarse, with short internodes, 
reddish purple in color. The leaves are large, thick, and 
greenish bronze with a tine edge of purple. The petioles 
are purple, and this color extends up on the veins of the 
lower side of the leaf. The roots are rose to red in color, 
spindle shaped to globular, with a tendency to grow large 
and irregular on very fertile soils, smooth, and without 
veins. The flesh is orange yellow to salmon, very sweet, 
and moist and soft in texture. 
The vines of the Dooley variety are slender and long 
growing. The roots are large in circumference, short 
spindle shaped, dark yellow to salmon, soft, and sweet. 
627. Climatic requirements. — There are extensive 
areas in the United States which are well adapted to 
sweet potatoes, mainly because of suitable climatic con- 
ditions. The plant is very tender and demands high tem- 
peratures. An abundance of sunshine is essential to 
high yields. Although a liberal rainfall is desirable dur- 
ing the growing season, it is detrimental when the tubers 
are maturing, because it encourages excessive vine 
growth at the sacrifice of tubers. There should be a 
growing season of not less than 4 months without 
frost. Warm nights are important to obtain the best 
results. This vegetable is often grown in northern gar- 
dens, but it is futile to attempt its cultivation commer- 
cially where climatic conditions are unsuitable. 
628. Soils. — The lighter soils are invariably regarded 
as the best for sweet potatoes. A moderate proportion 
of sand in the top soil, with a fairly retentive subsoil, 
provides ideal conditions. Whatever the soil type, it 
must be warm, loose and well drained. Stiff, heavy soils 
should never be planted with this vegetable. When it is 
necessary to use such soils in supplying sweet potatoes 
