Fig. 86.—The Making of Ordinary Boards, and One Way of Making “Quartered” Boards.
Beauty of grain and polish gives wood value for furniture, pianos, and the like. Mahogany and white oak are most beautiful, although red oak is also used. Oak logs which are first quartered and then sawn radially expose the beautiful silver grain (medullary rays). Fig. [86] shows one mode of quartering. The log is quartered on the lines a, a, b, b; then succeeding boards are cut from each quarter at 1, 2, 3, etc. The nearer the heart the better the “grain”: why? Ordinary boards are sawn tangentially, as c, c. Curly pine, curly walnut, and bird’s-eye maple are woods that owe their beauty of grain to wavy lines or buried knots. A mere stump of curly walnut is worth several hundred dollars. Such wood is sliced very thin for veneering and glued over other woods in making pianos and furniture. If the cause of wavy grain could be found out and such wood grown at will, the discovery would be very useful. Maple is much used for furniture. Birch may be coloured so as very closely to represent mahogany, and it is useful for desks.
Special Products of Trees.—Cork from the bark of the cork oak in Spain, latex from the rubber, and sap from the sugar-maple trees, turpentine from pine, tannin from oak bark, Peruvian bark from cinchona, are all useful products.
Suggestions.—Parts of a root and stem through which liquids rise. 49. Pull up a small plant with abundant leaves, cut off the root so as to leave two inches or more on the plant (or cut a leafy shoot of squash or other strong-growing coarse plant), and stand it in a bottle with a little water at the bottom which has been coloured with red ink (eosine). After three hours examine the root; make cross sections at several places. Has the water coloured the axis cylinder? The cortex? What is your conclusion? Stand some cut flowers or a leafy plant with cut stem in the same solution and examine as before: conclusion? 50. Girdle a twig of a rapidly growing bush (as willow) in early spring when growth begins (a) by very carefully removing only the bark, and (b) by cutting away also the sapwood. Under which condition do the leaves wilt? Why? 51. Stand twigs of willow in water; after roots have formed under the water, girdle the twig (in the two ways) above the roots. What happens to the roots, and why? 52. Observe the swellings on trees that have been girdled or very badly injured by wires or otherwise: where are these swellings, and why? 53. Kinds of wood. Let each pupil determine the kind of wood in the desk, the floor, the door and window casings, the doors themselves, the sash, the shingles, the fence, and in the small implements and furniture in the room; also what is the cheapest and the most expensive lumber in the community. 54. How many kinds of wood does the pupil know, and what are their chief uses?
Note to Teacher.—The work in this chapter is intended to be mainly descriptive, for the purpose of giving the pupil a rational conception of the main vital processes associated with the stem, in such a way that he may translate it into his daily thought. It is not intended to give advice for the use of the compound microscope. If the pupil is led to make a careful study of the text, drawings, and photographs on the preceding and the following pages, he will obtain some of the benefit of studying microscope sections without being forced to spend time in mastering microscope technique. If the school is equipped with compound microscopes, a teacher is probably chosen who has the necessary skill to manipulate them and the knowledge of anatomy and physiology that goes naturally with such work; and it would be useless to give instruction in such work in a text of this kind. The writer is of the opinion that the introduction of the compound microscope into first courses in botany has been productive of harm. Good and vital teaching demands first that the pupil have a normal, direct, and natural relation to his subject, as he commonly meets it, that the obvious and significant features of the plant world be explained to him and be made a means of training him. The beginning pupil cannot be expected to know the fundamental physiological processes, nor is it necessary that these processes should be known in order to have a point of view and trained intelligence on the things that one customarily sees. Many a pupil has had a so-called laboratory course in botany without having arrived at any real conception of what plants mean, or without having had his mind opened to any real sympathetic touch with his environment. Even if one’s knowledge be not deep or extensive, it may still be accurate as far as it goes, and his outlook on the subject may be rational.
Fig. 87.—The Many-stemmed Thickets of Mangrove of Southernmost Seacoasts, many of the trunks being formed of aërial roots.
CHAPTER XI
LEAVES—FORM AND POSITION
Leaves may be studied from four points of view,—with reference to (1) their kinds and shapes; (2) their position, or arrangement on the plant; (3) their anatomy, or structure; (4) their function, or the work they perform. This chapter is concerned with the first two categories.