When the soil is reasonably porous and fertile, a strong root may start at the seed-piece and descend more or less directly into the subsoil. In most cases, however, the roots spread laterally. This is a good illustration of how plants may vary in their root habits in order to adapt themselves to their environment. Notice where the roots form on the plants you are growing. Few farmers know where they form. Distinguish the true or feeding roots from the underground stems. Determine how many tubers form on each underground stem. Dig up a hill of potatoes from the garden before school closes.
Fig. 272. Underground part of potato plant in mellow soil.
Fig. 273. Piece of tuber for planting, bearing a single eye.
A single eye, with a portion of the tuber attached to furnish nourishment to the bud until sustenance can be secured from newly formed rootlets, may produce one, occasionally more, strong upright stems. A most interesting study of manifold reproduction may be made even in the winter time by planting in a fertile soil a piece of potato containing a single eye ([Fig. 273]). As soon as the rootlets begin to start, divide each eye and piece into two parts and re-plant. In a few days after the rootlets have again started, divide the two pieces into four and re-plant. This operation may be performed again and again, until many plants suitable for transplanting in the open may be secured from a single eye.
Demonstrate that the potato contains starch. This can be done by applying a drop of dilute iodine to a freshly cut surface of the tuber: the starch grains turn blue-black. Five cents' worth of iodine purchased at the drug-store will be sufficient for many tests. Dilute it about one-half with water. This starch, after being changed to sugar, supplies the young plant with nourishment. Dig up the pieces you have planted and see which start first, shoots or roots.
The "potato" is an enlarged underground stem provided with numerous buds similar to those on the stems of plants above ground. These buds are placed spirally on the underground stem or tuber with a considerable degree of uniformity. As on the stems of other plants, the buds are less numerous and weaker at the base and most numerous and vigorous at the top or upper end. On a smooth well developed long potato, the spiral arrangement of the buds may be illustrated by sticking a tooth-pick or pin in each eye, beginning at the base or stem end, and connecting the pins with a string ([Fig. 274]).
