SUGGESTIONS.—=55.= The pupil should match leaves to determine whether any two are alike. Why? Compare leaves from the same plant in size, shape, colour, form of margin, length of petiole, venation, texture (as to thickness or thinness), stage of maturity, smoothness or hairiness. =56.= Let the pupil take an average leaf from each of the first ten different kinds of plants that he meets and compare them as to the above points (in Exercise 55), and also name the shapes. Determine how the various leaves resemble and differ. =57.= Describe the stipules of rose, apple, fig, willow, violet, pea, or others. =58.= In what part of the world are parallel-veined leaves the more common? =59.= Do you know of parallel-veined leaves that have lobed or dentate margins? =60.= What becomes of dead leaves? =61.= Why is there no grass or other undergrowth under pine and spruce trees? =62.= Name several leaves that are useful for decorations. Why are they useful? =63.= What trees in your vicinity are most esteemed as shade trees? What is the character of their foliage? =64.= Why are the internodes so long in water-sprouts and suckers? =65.= How do foliage characters in corn or sorghum differ when the plants are grown in rows or broadcast? Why? =66.= Why may removal of half the plants increase the yield of cotton or sugar-beets or lettuce? =67.= How do leaves curl when they wither? Do different leaves behave differently in this respect? =68.= What kinds of leaves do you know to be eaten by insects? By cattle? By horses? What kinds are used for human food? =69.= How would you describe the shape of leaf of peach? apple? elm? hackberry? maple? sweet-gum? corn? wheat? cotton? hickory? cowpea? strawberry? chrysanthemum? rose? carnation? =70.= Are any of the fore-going leaves compound? How do you describe the shape of a compound leaf? =71.= How many sizes of leaves do you find on the bush or tree nearest the schoolroom door? =72.= How many colours or shades? =73.= How many lengths of petioles? =74.= Bring in all the shapes of leaves that you can find. [Illustration: FIG. 112.—COWPEA. Describe the leaves. For what is the plant used?] CHAPTER XII LEAVES—STRUCTURE OR ANATOMY Besides the =framework=, or system of veins found in blades of all leaves, there is a soft cellular tissue called =mesophyll=, or =leaf parenchyma=, and an =epidermis= or skin that covers the entire outside part. [Illustration: FIG. 113.—SECTION OF A LEAF, showing the air-spaces. Breathing-pore or stoma at _a_. The palisade cells which chiefly contain the chlorophyll are at _b_. Epidermal cells at _c_.]