Botany : specially written to meet the requirements of teachers' D, matriculation, public service entrance, intermediate and pharmacy A examinations

REPRODUCTIVE ORGANS

FIG.5 BEAN FLOWER FRONT VIEW [sketch with Standard, Wing, Wing, Keel, Sepal lobe, and Calyx tube labeled]

FIG. 6 SECTION [sketch with Standard, Keel, Wing and Sepal labeled]

FIG. 7 PETALS separated [sketch with Standard, Wing, Wing, and Keel labeled]

FIG. 8 PISTIL AND STAMENS [sketch with Nine united Stamens, style, Stigma, Ovary, and Free Stamen labeled]

FIG. 9 OPENED BEAN POD [sketch with Seed and Funicle labeled]

FIG. 10 OPENED BEAN SEED [sketch with Cotyledon, Plumule and Radicle labeled]

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summons from afar the birds that are to be its pollen bearers.

(d) Carpels. In the bean, there is only one carpel and this constitutes the pistil of the flower. To examine this, break away the tube formed by the lower parts of the nine united stamens. The lower thicker part of the pistil is called the ovary. Split this and notice the ovules, which later on develop into seeds. At the end of the ovary is a more slender portion, the style, which is bent at right angles, and whose function is to place the stigma, the sticky part at the tip, in a suitable position for receiving the pollen carried to it by visiting insects. In most flowers we find more than one carpel, and these carpels may be united or free. In the former case, collectively they form the pistil (Fig 8). In the buttercup and clematis the carpels are free and each has its own ovary, style and stigma. In the lily, the three carpels are united to form a single body, in which the ovary shows three chambers or cells, and the stigma spreads out into three lobes at the tip of the single style, which has been formed by the fusion of the styles of the three original carpels. Though the true function of the carpels is to produce and protect the seed we find that, in the iris, parts of them, the styles, are large and brightly coloured and thus assist the petals in their work.

2. The Fruit (Fig. 9) generally arises from the development of the ovary, though as we have seen in the tutu, neighbouring structures may take part in its composition. The bean fruit is a pod which consists exclusively of the developed ovary and has the seeds attached in a row by funicles or little stalks to its interior surface. The shell of the pod is formed of the ovary wall which has become tough and firm to protect the seeds. In many cases, as in the cherry and blackberry, the fruit becomes succulent, and birds,

eating it, pass the stone undigested, and thus serve to distribute the seed. There is a vast variety of fruits, dry or succulent, light or heavy, solid or hollow, opening or non-opening - all adapted to the particular surroundings in which the plant and its ancestors have lived. To deal with the modification of fruits would be to anticipate the whole subject, so that further discussion must be left for another place.

The Seed (Fig. 10) can hardly be called an organ of the plant. It is in reality the form in which the individual plant sets free its offspring to battle for itself. It is the young plant of the new generation, together with a store of food provided by its parent to tide it over the initial difficulties of getting into due relation with its environment, in other words to feed it till it can gather food for itself.

Remove the skin from the bean seed and split apart the two fleshy seed leaves or cotyledons, which contain the store of reserve material with which the young plant begins its development. Between the cotyledons appears the tiny plant, even at this early stage showing a differentiation into radicle or young root and plumule or young stem. Further consideration of the seed will be deferred till we deal with germination.

At this stage it may be well once more to insist on the need for field botany. The student should first make himself familiar with the weeds and other wild plants in his garden or playground, then study those in waste places and by the roadside, and finally make expeditions to the bush, the marshes, and the seashore further to extend his knowledge. It will at first be impossible in most cases for him to name the specimens himself (for even an expert botanist may find it hard to identify an

unfamiliar plant) but in almost every district there are a few enthusiasts, who will be only too glad to assist, and if all else fails, the author will render what help he can.

From this point onwards it will be well to alternate the lessons on special topics such as germination and growth, with a general study of one or more of such plants as may happen to be in flower. Material for this purpose will be found in the section dealing with natural orders which is placed at the end of the book. Familiarity with a large number of types, and the consideration of whole plants, alternately with the detailed study of special organs, gives that breadth which an exclusive attention to detail is not unlikely to destroy.

SUMMARY. Vegetative Organs. The Root obtains water containing dissolved mineral salts from the soil. The Stem conducts these to the leaves and carries the organic material manufactured there to the parts where they are required. The stem also spreads out the leaves to the air and sunlight. The Leaf, by means of its chlorophyll, uses the energy of the sunlight to build up organic compounds from the inorganic materials obtained from earth and air.

Reproductive Organs. The Flower consists of sepals which protect the young flower bud, of petals which attract insects, of stamens which produce the pollen, and of carpels which form the pistal and contain the ovules. The Fruit is the developed ovary, sometimes with the addition of neighbouring parts. It contains the seeds. The Seed is a young plant with a store of nourishment. Cotyledons, root and shoot are all present.

QUESTIONS ON CHAPTER I.

1. What is an organ? Name three organs found in animals and three found in plants. 2. What is meant by function? What are the chief functions of a bean plant? 3. Show that the bean plant is an organism. 4. When is the broad bean usually sown? When does it flower and when is the fruit ripe? 5. Contrast the root and stem of a bean plant, dealing with colour, shape, direction of growth, appendages, etc. 6. Sketch sections of the stem and root. 7. What happens when water is poured on a bean leaf? What does the result suggest to you? 8. Compare the bean leaf with that of any other plant. 9. Make sketches of a bean leaf. 10. What insects have you seen visiting the bean flower? Where do they alight? 11. What changes take place in the flower from the unfolding of the bud to the production of the ripe pod? 12. How does the bean pod open if left on the plant? 13. Draw a bean seed showing all the external features. 14. Take off the coat of a bean seed, separate the seed leaves and draw what you see. 15. What happens when a bean seed is soaked in water, and what when placed in the soil? 16. Show that all parts of a bean seedling are present in the seed. 17. Compare the seed-leaves of the bean with its foliage leaves. 18. Distinguish "Reproductive" and "Vegetative" organs. Classify the organs of a potato plant under these two heads and justify each item in your classification. 19. What is meant by environment? Justify the assertion that air, soil, water and climate are the most important factors in the environment of an ordinary green plant.