in the pea and bean family, in rosaceous plants and the family Rubiaceae. They are not common in dicotyledons with opposite leaves. Plants having stipules are called stipulate; those having none are ex stipulate. Stipules may be large or small, entire or divided, deciduous or persistent. They are not usually of the same form as the ordinary foliage leaves of the plant, from which they are distinguished by their lateral position at the base of the petiole. In the ans

FIG. 21.-Leaf of Orange (Citrus A urantium), showing a winged leafy petiole p, which is articulated to the lamina l. family Rubiaceae. I P Y (fig. 24) the true I leaves are stalked and crenate, while I the stipules s are - large, sessile and pin- natifid. In Lalhyrus 1 ' Aphaca and some J other plants the true pinnate leaves are abortive, the petiole forms a tendril, and I, the stipules alone are lx x developed, perform- ing the office of 1 leaves. When stipulate leaves are opposite to each other, at the same height on the stem, it occasionally happens that the stipules on the two sides unite wholly or partially, so as to form an irilerpetiolary or inter- foliar stipule, as in members of the n the case of alternate leaves, the stipules at it i N fl i Q ik My a, ,

FIG. 22.-Pitcher (ascidium) of a species of Side-saddle plant (Sarracenia purpurea). The pitcher is formed from the petiole, which is prolonged. the base of each leaf are sometimes united to the petiole and to each other, so as to form an adnate, adherent or petiolary stipule, as in the rose, or an axillary stipule, as in Houtluynia cordata. In other instances the stipules unite together on the side of the stem opposite the leaf forming an ocrea, as in the dock family (fig. 25). In the development of the leaf the stipules frequently play a most il/ Z

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i

gi, y, f»- L 1 5 important part. They begin to be formed after the origin of the leaves, but grow much more rapidly than the leaves, and in this way they arch over the young leaves and form protective chambers wherein the parts of the leaf may develop. In the figs, magnolia and pond weeds they are very large and completely envelop the young leaf-bud. The stipules are sometimes so minute as to be scarcely distinguishable without the aid of a lens, and so fugacious as to be visible only in the very young state of the leaf. They may assume a hard and spiny character, as in Robinia Pseudacacia (fig. 19), or may be cirrose, as in Smilax, where each sti ule is re resented b l l > P I-7 Y 3 tendril. At the base of the leaflets of a compound leaf, small stipules (stipels) are occasionally produced. Variations in the structure and forms of lllgaves and leaf; sta s are produce xsgnw' by the increased development of cellular tissue, by the abortion or degeneration of parts, by the if, W l"'7| its f/ gig ) "" ¢ A up 1 ), , »l ) Illllwl If I i FIG. 23.-Leaf of an heterophylla), showing a fattened leaf-like petiole p, called a phyllode, with straight venatio nate lamina. often increased by many horticultural culence of leaves. are rendered more development of parenchyma and tissue, leaves are The leaves of barber multiplication or repetition of parts and by adhesion. When cellular tissue is developed' to a great extent, leaves become succulent and occasionally assume a crisp or curled appearance. Such changes take place naturally, but they are gardener, and the object of to increase the bulk and sucway that cabbages and savoys nutritious. By a deficiency in an increase in the mechanical iable to become hardened and spineseent. ry and of some species of Astragalus, and the Acacia (Acacia n, and a bipinthe art of the operations IS It is in this delicate and stipules of the false acacia (Robinia) are spiny. To the same cause is due the spiny margin of the holly-leaf. When two lobes at the base of a leaf are prolonged beyond the stem and unite (fig. 26), the leaf is per foliate, the stem appearing to pass through it, as in Bupleurum perfoliaturn and Chlora perfoliata; when two leaves unite by their bases they become eonnate (Hg. 27), as in Lonicera Caprifoliurn; and when leaves adhere to the stem, forming a sort of winged or leafy appendage, they are decurrerit, as in I thistles. The formation of peltate leaves has been traced to the union of the lobes of a cleft I leaf. In the leaf of the Victoria regia the transformation may be traced during li. germination. The first leaves produced "I by the young plant " ' f are linear, the second are sagittate and hastate, the third ., are rounded-cordate and the next are? orbicular. The cleft indicating the union of the lobes remains in the large leaves. PUl@5~ 01 OCfea-The parts of the leaf are frequently transformed into tendrils, with the view of enabling the plants to twine round others for support. In Leguminous plants (the pea tribe) the pinnae are frequently modified to form tendrils, as in Lathyrus Aphaca, in which the stipules perform the function of true leaves. In Flagellaria iridica, Gloriosa superba I if I 'gr 1 *

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// ll FIG. 24.-Leaf FIG. 25.-Leaf of Polyof Pansy. s, Sti- gonum, with part of stem. W, ,.~. /fi *ii Ni ' “ .: “mU l, ' lg: aw wflixi. . '-; W"W& if ~ T vt I I ;l|“.';':§

FIG. 2e.~Peff01iat@ leaf of a species of Hare's-ear / (Bupleururn roturidifoliurn). The two lobes at the base of the leaf are united, so that the stalk appears to come through the leaf. FIG. 27.-Connate leaves of a species of Honeysuckle (Lonicera Caprifolium). Two leaves are united by their bases. and others, the midrib of the leaf ends ui a tendril. In Srnilax there are two stipulary tendrils. The vascular bundles and cellular tissue are sometimes developed in such a way as to form a circle, with a hollow in the centre, and thus give rise to what are called jistular or hollow and to aseidia or pitchers. Pitchers are formed either by petioles or by laminae, and they are composed of one or more leaves. In Sarracenia (fig. 22) and Heliarnphora the pitcher is composed of the petiole of the leaf. In the pitcher plant, Neperzthes, the pitcher is a modification of the lamina, the petiole often plays the part of a tendril, while the leaf base is flat and leaf-like (fig. 28). In Utricularia bladder-like saes are formed by a modification of leaflets on the submerged leaves. In some cases the leaves are reduced to mere scales-ealaphyllary leaves; they are produced abundantly upon underground shoots. In parasites (Lathraea, Orobariche) and in plants growing on decaying vegetable matter (saprophytes), in which no chlorophyll is formed, these scales are the only leaves produced. In Pinus the only leaves produced on the main stem and the lateral shoots are scales, the acicular leaves of the tree growing from axillary shoots. In Cycas whorls of scales alternate with large pinnate leaves, as in the onion, xv

l' 5 I i7 J > in if-, 'ZH I, //) / A I FIG. 28.-Pitcher of a species of pitcher-plant (Neperithes distillatoria). leaves. In many plants, as already noticed, phylloclia or stipules

perform the function of leaves. The production of leaf-buds from