mentioned those of the Vetch (Vicia sativa), which secrete honey, especially when the sun shines. The stipular glands of Viburnum have been already described (ante, p. 40). In the Myrtaceae, again, we have cases of glandular stipules. In Psidium Cattleyanum they consist of one to four subulate processes, or of one rather membranous and colourless, trifid or tridentate piece. They scarcely FIG. 312.-TROPÆOLUM CILIATUM, showing leaf and stipule. Nat. size. seem to be protective, but the outer process is generally tipped with a globule of fluid. The remarkable Peruvian species of Tropaeolum already mentioned (T. ciliatum) has curious ciliated and apparently gland-tipped orbicular stipules (fig. 312). Glandular stipules also occur in some Lythrarieæ, Leguminosa, Linacea, Onagrarieæ, Cucurbitaceæ, Droseraceae, Balsams and Cruciferæ. AS AN ASSISTANCE IN CLIMBING There are two ways in which stipules may assist in this respect, viz. (1) by being developed into tendrils, or (2) into more or less reversed spines. St B The case of the tendrils of Smilax is one which has occasioned much St discussion, but I agree with Tyler Sc" (24) that the embryological, together with the anatomical, characters indicate that in Smilax the tendrils are true stipules, found in connection with the sheathing petiole. St St St B St Sc' FIG. 313. - PALIURUS St, St, spiny unequal sti- In Paliurus australis (fig. 313), a Southern European plant belonging to the same family as our Buckthorn, the stipules are spiny, but the two stipules of each leaf are different in form and serve for different purposes. Those on the upper side of the shoots are long, subulate, and straight; those on the lower side are shorter and deflexed. The former appear to serve as a protection against of which is spiny: Sc', browsing quadrupeds; while the scar of fallen petiole; Sc", the third scar in showing that the phyl the order of arrangement, lotaxy is. Nat. size. hooked ones also assist the plants to climb or scramble up among other shrubs and bushes. In Macharium also, a tropical American genus of Leguminosa, the stipules are often converted into thorns, which are in some cases bent backwards so as to aid the plant in climbing. AS RESERVES OF NOURISHMENT In Gunnera, according to Reincke (25), stipules serve as reserves of nourishment. AS HOLDERS OF RAIN Another use of stipules is to hold rain, as, for instance, in some species of Thalictrum, Viola, and Polygonum. The leaflets of Thalictrum (T. simplex) are so arranged as to catch most of the raindrops; they are not wetted, however, by the rain, which runs off and down the petiole to the cup formed by the stipules. The stipules are fringed at the edge, which also assists to retain the moisture. In some species of Viola also—for instance, Viola tricolor (Pansy) and the little yellow V. biflora-the leaf and leaf-stalk have a central furrow, down which the water runs to the stipules, by which it is retained. The ocrea or sheath of the Polygonacea also serves in some cases for the same purpose. This is well seen in the large species, for instance, of Rumex and Rheum. They will retain water for several days after the rain has ceased. It is, however, gradually absorbed. In support of this view I may refer to the case of the Teasel (Dipsacus), where the bases of the petioles are expanded and connate, thus forming a large cup, which generally contains water. It has been suggested by Kerner that this water forms a sort of moat, which protects the flowers from ants and other creeping insects. On the other hand, Mr. Francis Darwin suggests that insects, &c., are drowned in the water, and thus supply the plant with animal food. He has described certain curious protoplasmic threads, emitted by some of the cells, which he suggests may serve to absorb the nourishment thus supplied. AS SUPPORTS It is probable that, as Grevillius (26) has suggested, the ocrea of Polygonum may be of use in strengthening the stem at the internodes, which are points of rapid growth, and consequently of weakness. He observes that this can be tested by removing the sheath, and then shaking the stem, when it will be found that it is especially liable to give way at the internode. 197 CHAPTER VIII ON THE NATURE OF STIPULES IN ordinary parlance, when we speak of a leaf we often think only of the leaf-blade. The leaf-blade is, however, in reality only part of the leaf. The complete leaf is generally described botanically-as, for instance, in Asa Gray's excellent 'Structural Botany,' Bentham's 'Handbook of the British Flora,' &c.--as consisting of (1) the leaf-blade, (2) the stipules, and (3) the petiole or stalk, to which I think, for reasons which will be presently given, we ought to add (4) the leaf-base. Vines (27) describes the leaf as divisible into three transverse parts-upper, median, and lower-corresponding to the blade, stalk, and base. The base may, he considers, be either more or less sheathing, or developed laterally, forming stipules. The stipules, however, seem to occupy the same position in relation to the base as the blade or leaflets do to the stalk. If, therefore, the blade is considered as forming a division separate from the stalk, I should rather regard the leaf as consisting of four parts: the blade, stalk, stipules, and base. Perhaps, however, the more philosophical view would |