13. Make a list of plants which you have observed to climb by twining stems, and note whether they are clockwise or counter-clockwise climbers. 14. Make careful drawings of all the tendrils you can find, and try to discover which part of the plant has been modified to form the tendril. 15. Gently stroke a tendril of the passion flower and write an account of any resulting movement. 16. Mention any three climbing plants which grow wild in this country, and explain in each case how the plant climbs. (1895) 17. What is the difference between (a) a thorn, (b) a leaf-spine, and (c) a prickle? Give examples. (1896) 18. Enumerate and briefly describe the principal varieties of tendrils, and explain how they act. (1897) 19. If a wire is fastened tightly about a growing branch of a common tree, and left for two or three years, what effect will be produced, and how can the effect be explained? (1904) 20. What processes of vegetable growth are accompanied by the presence of sugar? Give examples from plants within your own experience. (King’s Scholarship, 1904) 21. What are the chief uses of the vessels of a herbaceous stem? Mention observations and experiments in support of your statements. (1905) 22. How can you demonstrate experimentally that food substances, formed in the leaves of a tree, descend to the branches below? (1905) [Pg 88] CHAPTER VI. SOME COMMON FLOWERS. 15. A TYPICAL FLOWER. I. The wallflower.—After noticing the general habit of growth of a wallflower plant (Fig. 57), and especially the shape and venation of the leaves, make out the following parts in one of its flowers. On the top of the flower-stalk (called the receptacle) are: Fig. 57.—Wallflower. (× ⅙.) (a) Four small, narrow, purplish leaves, called sepals. The four sepals together constitute the calyx. Take off the sepals one by one. Notice that two opposite sepals are bulged out at their bases, forming pouches containing nectar. Try to get out a small drop of nectar on the point of a pencil and taste it. (b) Four showy leaves arranged in the form of a Maltese cross, called petals. They are yellow, or red, or purplish in colour, are [Pg 89] delicately scented, and have beautiful velvety surfaces. The four petals together constitute the corolla. Take off the petals one by one. (c) Six stamens, each consisting of a greenish stalk or filament surmounted by a yellow, boat-shaped body, called the anther. The anther is a four-chambered box containing an enormous number of tiny yellow grains called pollen grains. Two of the stamens are shorter, and are fixed at a lower level on the receptacle than the remaining four. Take off the stamens one by one.