Roots play yet another important part in the plant’s life-history, by receiving and storing food that has been made in the. The that we use as food storage of contain the greatest store. The Carrot, Turnip, Beetroot, and Radish are swollen with reserve supplies.
All these plants are. In the first year of their growth they bear no . The whole energy of the plant is concentrated upon food manufacture in the . The manufactured food, in soluble form, is then carried down the through the tissue known as bast, or phloem, and so reaches the for storage. The following spring the plant produces as well as leaves, and fruit- and -formation follow. There is a great demand for food for all these rapidly growing parts. The demand is met by the supply stored in the .
If at this period such swollen tap-are used as food, they are tasteless, tough, and stringy. The plant has made use of its own reserves, and there is nothing left for us.
As soon as theare set, in the second year, the whole plant dies. Its life-history is completed.
It is not only the obviously swollen roots that hold food reserves. Possibly with the exception of roots ofand adventitious roots of underground , all roots contain a certain store. This was instanced in the power of the Fuchsia root to continue its pumping action for several days, although it was receiving no fresh supplies of food.
In the autumn, before all the aerial parts of herbaceous perennials die down, the food manufactured by the leaves is deposited in the roots. For this reason young shoots of, Monkshood, Snapdragon, Columbine and the like, grow up rapidly in the springtime ; each has a store of food to draw upon, just as surely as the embryo of the germinating has its reserve supply.
The Carrot, Beetroot, and the like are swollen tap-roots.
The ordinary tap-root is typically seen in a germinating Broad Bean. It is a long root that grows straight down into the ground on a line with the main stem.
It tapers to a point (possibly this may be the origin of the name) and bears branch roots that are shorter and finer than the main root from which they spring. But it is only in size and direction of growth that the branches differ. In structure they are the same as the parent axis, because roots, unlike stems, only bear lateral appendages that are similar to the main root. Hence a root does not bear leaves.
In beans that have germinated in gas-jars the secondary roots leave the main root almost at an angle of 90 degrees. When plants produce tertiary roots they may often come off at an angle of about 45 degrees In the soil this arrangement may be interfered with by various obstacles, but the point to notice is, that it is only the main root that obeys the pull of gravity by growing vertically downwards.
On the main root and its branches, a short distance behind the root-tip, are the numerous white, plush-like root-hairs.