SUGGESTIONS.—_To study epidermal hairs_: =75.= For this study, use the leaves of any hairy or woolly plant. A good hand lens will reveal the identity of many of the coarser hairs. A dissecting microscope will show them still better. For the study of the cell structure, a compound microscope is necessary. Cross-sections may be made so as to bring hairs on the edge of the sections; or in some cases the hairs may be peeled or scraped from the epidermis and placed in water on a slide. Make sketches of the different kinds of hairs. =76.= It is good practice for the pupil to describe leaves in respect to their covering: Are they smooth on both surfaces? Or hairy? Woolly? Thickly or thinly hairy? Hairs long or short? Standing straight out or lying close to the surface of the leaf? Simple or branched? Attached to the veins or to the plane surface? Colour? Most abundant on young leaves or old? =77.= Place a hairy or woolly leaf under water. Does the hairy surface appear silvery? Why? _Other questions_: =78.= Why is it good practice to wash the leaves of house plants? =79.= Describe the leaf-scars on six kinds of plants: size, shape, colour, position with reference to the bud, bundle-scars. =80.= Do you find leaf-scars on monocotyledonous plants—corn, cereal grains, lilies, canna, banana, palm, bamboo, green brier? =81.= Note the table on page =88.= Can you suggest a reason why there are equal numbers of stomates on both surfaces of leaves of tradescantia and flag, and none on upper surface of other leaves? Suppose you pick a leaf of lilac (or some larger leaf), seal the petiole with wax and then rub the under surface with vaseline; on another leaf apply the vaseline to the upper surface; which leaf withers first, and why? Make a similar experiment with iris or blue flag. =82.= Why do leaves and shoots of house plants turn towards the light? What happens when the plants are turned around? =83.= Note position of leaves of beans, clover, oxalis, alfalfa, locust, at night. CHAPTER XIII LEAVES—FUNCTION OR WORK We have discussed (in Chap. VIII) the work or function of roots and also (in Chap. X) the function of stems. We are now ready to complete the view of the main vital activities of plants by considering the function of the green parts (leaves and young shoots).