STRUCTURE OF PLANTS

Hokitika Guardian, 13 July 1929, Page 7

STRUCTURE OF PLANTS

THE FOUNDATION OF BOTANY. INSTRUCTIVE LECTURE. An interesting address on the “ General Structure of Plpnts ” and the functions of those structures was given to W.E.A. students in horticulture on Friday evening at the Trades Hall, Wellington, by Mr M. Davey, of the Department of Agriculture. He said that the subject was a very wide one, which represented one of the foundations of modern botany, and that -■‘all plants, except those of the lowest order, consisted of unions of innumerable microscopic structures called cells. The lowest- form of plant life was composed of a single cell. The cell wall consisted of a substance known as celluose, and this farmed the framework or skeleton of all-plants. It was lined with protoplasm, which in very young cells entirely filled the cell cavity, and this substance was present wherever there was life of a complex composition, and it contained carbon, hydrogen, oxygen, nitrogen, and sulphur. “ Amongst other protoplasmic bodies is nucleus,” said Mr Davey, “and this appears to be specially concerned in the reproductive processes, while to these smaller dense bodies generally the plants owe their colours, the green of which are called chlorophyll grains.

SUBDIVISION OF CELLS. “In -the growing region of plants an increase in the number of cells takes place ns a result of the division of previously existing cells, and the cells that constitute a plant are termed plant tissues,” continued Mr Davey. He explained the names and functions of the various kinds of tissues and dealt with the general structure of roots. He distinguished between tiny rootlets and root hairs, which were often confused with each other, and stressed the importance of the latter, as they took in the food materials from the soil. The process of osmosis also took place through the root hairs, which exerted the acid from the minerals used for plant nutrition. They were deve loped a short distance behind the point of the root and disappeared from the older parts. “Their wailed tube-like structures may be observed as a white silky band on the root of seedlings germinated on moist flannel of bloot-ing-paper,” said Mr Davey, “and they are seldom seen on the plant which has been removed from the soil because they are so delicate that they become broken off when the plant is lifted. Plants growing in wet situations have few or no root hairs, while in dry soils their development is alsr checked.” In dealing with stem struc ture Mr Davey mentioned the uses, of bark in protecting the plant from ex treme temperature, preventing loss of water and assisting in the _ admission of air, and the process that takes place in the healing of the wound on the ex posed portions of a tree.

BUDS AND LEAVES.

M,r Davey explained bud formation and detailed carefully leaf foliage and its functions, stressing the importuneof.light as an essential factor in pro viding the necessary food for the leave? of the plant. “ All the energy of ani mal food, of wood and of coal,” said the lecturer-, “ arise directly or indirectly from the carbon fixation which' takes place in green leaves. The red rays are the ones chiefly concerned ii the process, and as these are absorbed by the green colouring matter in leav*s light which has passed through a- leaf is practically useless for vegetation. Thus one crop will often not grow wel in the shade of another, as the dense crop shuts off the supply of direel light to the smaller plants, causing them to decline in vigour and ultimately die away. The same thing happen l with the lower branches of trees in forest plantations.” The importance of carbon-di-oxide in the air surrounding the leaves of a plant was referred to, also the respira tion which takes place not only in the 'eaves but in all parts of living plants. The action of giving off moisture i? known as transpiration, and it is a continuous and invisible process which would soon result in the death of tb* plant if it were not counter-balanced by the absorption of moisture from tin soil by the roots. The leaves of tin plant carry out similar functions to tin lungs and stomach in the animal kingdom.

USE OF THE FLOWER. In passing on to the study of the flower, Mr Davey stated that it was specially adapted for the production of seed in order to reproduce the plant. By watching and dissecting flowers at different stages of development the ■formation of the organs and seed’s could be noticed and as ripe seeds could not be produced without pollination it was possible to prevent this by cutting away the auttiers at an early stage and excluding any wind or in-sect-borne pollen by paperbagging the blossom. The processes of self-polli-nation and cross-pollination were exnlained, and the agencies used for trannortation .such ns insects, wind water and gravitation. The causes and effects of non-fertilisation were next dealt with, and reference was made fo the injury to the pollen or stigma that occurs through frost, rain or hail. The lecturer concluded a very helpful ad dress by explaining the difference I>etween fruit and seed and pointed out. that the formation and production of seed exerted a greater strain on tho vitality of a plant than the ordinary production of fruit. Lantern slides were shown in illustration.