. Elements of botany. Plants. 90 ELEMENTS OF BOTANY. 117. Stipules. — Although they are absent from many leaves, and disappear early from others, stipules form a part of what the botanist regards as an ideal or model leaf.^ When present they are sometimes found as little bristle-shaped objects, at the base of the leaf as in the apple leaf (Fig. 71), sometimes as leaf-like bodies, for example in the pansy (Fig. 72), and in many other forms, one of which is that of spinous appendages, as shown in the common locust (Fig. 76). 118. Relation of Venation to Shape of Leaves.—As soon as the student be
. Elements of botany. Plants. 90 ELEMENTS OF BOTANY. 117. Stipules. — Although they are absent from many leaves, and disappear early from others, stipules form a part of what the botanist regards as an ideal or model leaf.^ When present they are sometimes found as little bristle-shaped objects, at the base of the leaf as in the apple leaf (Fig. 71), sometimes as leaf-like bodies, for example in the pansy (Fig. 72), and in many other forms, one of which is that of spinous appendages, as shown in the common locust (Fig. 76). 118. Relation of Venation to Shape of Leaves.—As soon as the student begins to observe leaves somewhat widely, he can hardly fail to notice that there is a general relation between the plan of venation and the shape of the leaf. How may this relation be stated ? In most cases the principal veins follow at the outset a pretty straight course, a fact for which the student ought to be able to give a reason after he has performed Exp. 25. On the whole the arrangement of the veins seems to be such as to stiffen the leaf most in the parts that need most support, and to reach the region near the margin by as short a course as possible from the end of the petiole. 119. Parallel- Veined Leaves. — The leaves of many great groups of plants, such as the lilies, the sedges, and the grasses, are commonly parallel-veined, that is, with the veins running nearly parallel, lengthwise through the blade, as shown in Fig. 73, or with parallel veins proceeding from a midrib and then sending off parallel veinlets, as shown in Fig. Fig. 73. — Parallel- Veined Leaf of Sol- omon's Seal. 1 Unless the elm twigs used in the previous study were cut soon after the unfold- ing of the leaves in spring, the stipules may not have been left in any recognizable Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectplants, bookyear1896
