PATER’S CHATS WITH THE BOYS.

Otago Witness, Issue 3818, 17 May 1927, Page 10

PATER’S CHATS WITH THE BOYS.

THE NUTRITIVE ORGANS OF PLANTS.

The words “elementary botany” mean simple ideas about plant life, by means of which a foundation may be laid for a wider and deeper study of plants, their habitat, their life history, and the distinguishing marks or characteristics of their genera and species. The matter of to-day’s chat is about the way plants feed themselves, and involves observation and comment upon those parts of the plant which are concerned in the supply of food for the whole growing organism. All land ■ plants have three main parts—roots, stems and leaves; but all do not produce flowers and seeds. Seeweeds have what is called a root, but it is only an enlarged or swollen .end for gripping rocks. The difference between the root of a land plant and the root —properly the butt —of a seaweed, is that the roots of land plants not only hold the plant in position as does the butt of a seaweed, but, also, act as feeders. Someone may doubt whether certain plants, such as turnips, radishes, rhubard, onions, etc., have stems, but the bulbs or bulbous part of such plants and many humbler plants are really modified stems. It may also be said that this is not true, for if turnips and such like plants are allowed to go to seed, they then -show the real stem.. As a matter of fact, what they then develop is the flower stem or spike. ■When the plantlet of a monocotyledon or a dicotyledon has consumed the nourishment .stored up for it in the seed, it has to seek for other food in the neighbouring earth and the surrounding air. For the purpose of gathering materials suitable for sustaining life and growth, converting it into proper food form, and finally assimilating it in the same way as the animal body does the products of its stomach and intestines, the plant or tree uses three separate sets of organs or instruments—roots, stems, and the leaves.

When the plantlet has finished the fleshy part of the seed, it develops root hairs which have really a sense of touch and taste. The extremities of these root hairs are whitish, fleshy, and very delicate, and under a magnifying glass are spongy looking-; they are therefore called spongioles. In their search for food they shoot out in every direction, instinctively feeling- their way between and around stones and other obstacles till the proper medium on which to feed is found. They sense dampness, and will always extend themselves more vigorously towards a damp spot than towards a dry spot. If they reach the sides of a pond, well, or any kind of watery reservoir, they will spread and multiply with amazing rapidity.

Trees and shrubs develop a trunk stem, which, both above ground and below, develops branches which, as the plant grows, become woody and thicker. Underground the root stems send out rootlets corresponding to the twigs or branchlets above ground. The spongioles, the suckers or feeders, in their search for food, are the intelligent directors of the spread of hard woody root branches. They seek water,

| for in the water underground is dissolved | from the rock material constituting the soil the chemical substances necessary for the food and life of the tree. If water or dampness is lacking in the soil no plant can grow even though all other conditions are suitable. The spongioles absorb liquid, which is conveyed along the root hairs to the woody fibre of the roots. In the woody tissues are living cells of starchy material, very complex in their formation. By some power within their bodies they take what they want as food and pass onward and upward by some mysterious directive power and intelligence the surplus of mineral food until the leaves are reached, every cell in the trunk taking what share it needs for its life existence. As time goes on the cells in the centre of the stem of the tree die, and what is called heart-wood is formed. In some trees as, for instance, our broad-leaf, the heart wood decays and the trees become holloow, while in others, like the kauri and black and red pines, it remains solid as a strong and somewhat elastic support for the rest of the trunk and branches. The process by which the liquid called sap, which the I spongioles gather, is passed up the trunk is supposed to be capillary attraction, that is. the power of fine tubes or very confined spaces to suck up liquids, in the samq way as a small mass of sugar absorbs a drop of water or blotting paper sucks up ink. But there is more in the work of these living starch cells than in the dead mechanical action of capillary attraction. No doubt the cells are Glided by capillarity, but the process of passing up the san is more elaborate. Active living work is there all right; otherwise the flow of sap would not be greater in spring p nd summer than it is in winter. Trees hibernate in winter just as do certain animals, and in many the san ceases for a period to flow upwards. The vivifying rays of the sun pf spring and summer are alwavs necessary to stimulate cell activity in all plants. Every cell is a little chemical worker, and sunlight and heat are required for the chemical changes which are made in the substances absorbed by the roots. In connection with the root feeding of plants there is an important fact to bo noted. Tree plants when the space round the root hairs is exhausted of food materials extend their root branches further afield seeking new feeding; but grasses, not having root branches canable of indefinite lengthening, are unable to seek new feeding places. Consequently they exhaust the soil near their roots and die. 'J hat is whv so many of our plants are what is called “annuals.” plants which live only a year; and that is also the reason why a crop of wheat, oats, or barley will not do well if planted a second year on the same ground unless something is done to restore the plant-food elements to the exhausted soil. Farmers know this, and all wise farmers owning l stock and farms take the precaution of either manuring the soil well before going in for a second crop; or if it suits their purpose better, going in for rotation of crops and other tricks of their trade, the knowledge of which has been gained by experience which has been handed down from sire to son through the ages. But farming is not the subject of this discourse, so we will return to the subject from which we have slightly digressed. Root crops, their nature, and sustenance is a special line of study in the art of fanning. £ll plant life is the study of the botanist.

As said before, every plant lias a stem or the vestige of a stem. When it is necessary for the life of the plant, the stem seeks an upright position to spread its branches, leaves, and flowers out in the air and to the sunlight. In the case of trees the stem is called the trunk, and the stems of all plants are divided according to their mode of growth into three classes exactly to the three classes of plants which are determined by the structure of the seed. The stem of our timber trees and all those shrubs or plants described as dicotyledonous, increases outwards, a new layer of woody matter being added every year just behind the bark. When the trunk is sawn across, these layers form distinct rings which can be counted and the age of the tree thus exactly determined. Such stems are termed exogenous, and the trees exogens. The hardest part is in the centre —the heart wood.

The stems of monocotyledons increase inwardly and quickly run to length, and are therefore termed endogenous or endogens. In their structure the hardest part is the outside. They have no separable bark, and as a general rule no branches.

Similar to them in most respects are the stems of acotyledonous plants like the fern tree, which, altering little in thickness of the stem as it is formed at the base, increases chiefly by additions at the crown or top. The term applied to them is acrogenous. Whatever their nature and their peculiarities in producing a stem, they all have one purpose, and that is to present their leaf surfaces to the light and heat of the sun to procure his assistance in their life activities.

The leaves of plants in a way. quite different from the roots, carry on the process of nutrition. In shape and appearance the leaves of plants vary tremendously with every species and variety of species ; but what is curious or remarkable, a classification of plants according to the texture of their leaves would nearly coincide with two of the classifications already mentioned. Exogens have leaves in which is a strong main rib and sometimes branches, where the veins cross and recross, forming a perfect network. This network can be seen in leaves out of which the fleshy green matter has decayed after the leaves have lain a considerable time on_ the- ground. In endogenous plants the veins run more or less parallel from the base to the tip. With very slight modification this venation is similar in aerogens. Examine the venation of a sycamore leaf or that of any timber tree, compare the venation with that of a blade of grass, a flax leaf, or the leaves of any lily, and note the difference between types of exogens and endogens. Leaves as well as root spongioles have little mouths—stomata—on the under side. By means of these they feed and exhale the excess moisture which the roots send up They extract food from the carbonic acid which permeates the atmosphere. In the sunlight each leaf is busy inhaling carbonic acid gas, or CO2, and decomposing it into its elements, carbon and oxygen. The carbon is retained to make wood and the oxygen is given off. The leaves are chemical laboratories in which the carbon separated out is combined again with material sent up from the roots into organic compounds sent by a circulation process back into the tree to build up its woody tissue. . The green of leaves is due to a substance known to students of organic chemistry as chlorophyl, which reacts to waves of light and heat from the sun and

gives energy to the living cells in the leaf, the little chemists which do the mysteriously wonderful work of inhalation and exhalation for the tree, and also the work of turning carbon, hydrogen, and mineral elements into liquid compounds • upon which the living cells of the tree can' feed. A well-known botanist said: “We can examine the organs of a plant and see the results of their action ; but who can tell the real nature of those processes by which the purpose of their existence is attained?” A boastful naturalist ordered t-> be inscribed on his statue— ‘‘ A genius equal to the majesty of Nature,” —a vain boast, for it has been well remarked that the wonder and mysteries of a single blade of the humblest grass were sufficient to disprove and confound his foolish pretensions.