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. [Illustration: 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 (1) to 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. [Illustration: FIG. 88.--A SIMPLE NETTED-VEINED LEAF.] [Illustration: FIG. 89.--A SIMPLE PARALLEL-VEINED LEAF.] [Illustration: FIG. 90.--COMPOUND OR BRANCHED LEAF OF BRAKE (a common fern).]