Cuttings are obtained from the stems of plants at least ten months old and 2.53.5 cm thick. After harvesting, these stems are stored in a dry place until the next planting (Fig. 5). Cuttings about 25 cm long should be taken from the lower 75150 cm of the stem after the first 20 em have been discarded. Cuttings from the upper part of the stem will grow faster, but their final yield is less. The best practice is to saw a bundle of stalks supported by a girder and then to point the cuttings thus obtained at the lower end (Fig. 6), taking care not to bruise the buds or otherwise damage the stem.
Experiments in the Philippines on the relation between the age of cuttings and yields showed that cuttings taken 75 cm or more below the apex of the stem gave the best starch yields. Other experiments concluded that older wood from the basal areas to the midpoint of the stems outyielded apical propagating material.
Key to Figure 4:
Left upper quadrant. after staining with iodine:
1a. Outer cork layer
1b. Inner layer
4. Pith and primary xylem
(Both peel and pith contain comparatively little starch.)
Right upper quadrant, showing structural elements of the root:
6. Sclerenchymatous fibres
7. Latex vessels
9. Xylem vessels
Inset A - Enlarged cross section of peel:
10. Cork tissue
11. Sclerenchymatous fibres
12. Starch (small grains)
13. Parenchyma cell
Inset B - Enlarged cross section of centre:
14. Cell wall (larger cells than in peel)
15. Starch ( big grains)
Cuttings are planted by hand or by planting machines. Hand planting is done in one of three ways: vertical, flat below the soil surface or tilted 45" from ground level. Under low rainfall conditions. vertical planting may result in the desiccation of the cuttings, while in areas of higher rainfall, flat-planted cuttings may rot. In general, flat planting 5-10 cm below the soil surface is recommended in dry climates and when mechanical planting is used. Germination seems to be higher; tubers tend to originate from a great number of points and grow closer to the surface of the soil, making better use of fertilizers applied on the surface and also making harvesting easier. On the other hand' vertical planting is used in rainy areas and tilted planting in semi-rainy areas.
The cuttings are planted on flat soil or on ridges or hills. Some experiments have shown ridging to produce somewhat lower yields than flat cultivation; but the work of weeding and harvesting is greatly reduced by ridge planting. As machine planting would be impossible with furrows or on ridges, flat fields are the most desirable. Spacing between rows is about 80100 cm, and the plants are spaced along the rows according to local conditions. The number of plants per hectare varies in different regions between 10000 and 15000.