YAM CULTURE IN PORTO RICO. 5 
for the succeeding crop may be left in the soil until planting time 
the following spring. In this way good seed may be preserved from 
decay. Clean seed is an important factor in establishing a good 
stand of new plants. Should a drought follow planting, the root 
sections, if they are free from decay, will remain in good condition 
for many weeks, owing to the thick corky covering of the yam, 
which enables the seed pieces to retain for a long time sufficient 
moisture for the growth of the plant. 
The yam, though very resistant to severe drought, requires a heavy 
rainfall for its best production. The plant does not have an ex- 
tensive root system, nor roots that work deep into the earth, yet it 
secures sufficient moisture to carry it through long rainless periods. 
This is observed along the southern and western parts of Porto 
Rico, where the vines make a moderate growth and show no effect 
from a drought which injures other vegetation. 
In preparing the land for planting care should be taken to 
bring the soil into good mechanical condition. Substantial ridges 
or hills should be made, to protect against excessive soil moisture 
and to secure good aeration of the soil. An excess of water in the 
soil invariably results in a crop of poorly developed roots. The 
deep-rooted varieties when grown in heavy unloosened soil are rather 
angular and irregular in shape, and the production is small. 
To avoid such results, ridges of loose earth and vegetable matter 
should be constructed from 1 to 1J feet high, depending upon the 
locality and the subsoil drainage. These ridges should be made 
by plowing the land deeply and thoroughly and by opening a wide 
furrow over which the ridge is to be made. In this furrow a few 
inches of dead vegetable matter should be placed and covered with 
2 or 3 inches* of earth. This should be followed by another layer 
of vegetable matter, the layering being continued thus until the 
ridge is finished. As the vegetable matter decays it causes a set- 
tling of the earth. The beds should, therefore, be made a few inches 
higher than otherwise would be necessary for the growth of the 
plants. 
These ridges may be cheaply constructed with a plow, the 
only hand labor needed being in the application of the vegetable 
matter and the final rounding up of the ridge with hoes. The 
layers of manure or other vegetable matter in the ridges insure a 
loose, well-aerated medium for the development of the roots, and 
seem to be required for their best development. The ridges do not 
need to be large in sand or sandy loam unless the subdrainage causes 
poor aeration of the strata occupied by the roots. In these soils 
the humus-providing material should never be omitted. 
When seed is scarce, either crowns or entire small tubers may be 
successfully used, or a cross section of a slender, cylindrical root 
