Goebel's experiments. In each case two seeds of the same weight were sown together : Normal Plant. After Removal 561 Plant 1. Stipule of 1st leaf measured 141 mm. It is probable, however, that more effect would be produced if the leaf had been extirpated at an earlier stage. In other species no corresponding effect followed. The suppression of the stipules in Lathyrus Aphaca, for instance, had no effect in transforming the tendrils into leaf-blades. Cotyledons very rarely have stipules. This may, perhaps, be because they are sufficiently protected by the fruit and seed coverings. There are, indeed, a few exceptions, as, for instance, in Genipa clusiafolia (figs. 335-338), where, however, they are very small. They are interpetiolar, united into one ovate, acute piece, colourless and subscarious. They occur also in Psychotria (fig. 339), another genus of Rubiaceae, a family of which one of the most constant characters is the presence of stipules. Another instance is afforded by Thelygonum. Clos, in an interesting and elaborate memoir (38), has attempted to show that as a rule bracts are modified stipules. De Candolle in 1858 expressed this opinion as regards Begonia; and Clos, amongst other species, refers to Cinchona officinalis and angustifolia, Isertia FIG. 335.-Longitudinal section of seed, x 23; C, cotyledon; R, radicle; En, endosperm. coccinea, Berteria guianensis, Spermacoce calyptera, Cissus tamoides, Rondeletia obovata, &c. Most of his references, however, are to old and somewhat vague figures. Cinchona officinalis has small but wellmarked stipules at the base of the bracts, and the same is the case in Rondeletia obovata. If bracts really represented stipules they would, as a rule, be in pairs, which is not the case. Moreover, Clos's view could not, of course, apply to the bracts of exstipulate species. FIG. 339. SEEDLING OF SPECIES OF PSYCHOTRIA. Nat. size. S, stipule. I think, then, as already stated, we must conclude that stipules are an integral part of the leaf; that leaflets are portions of the leaf-blade; and that, if we consider the leaf-blade as a part separate from the petiole, we must regard the leaf as consisting of four parts, viz.: 1. The blade. 2. The petiole. 4. The base. Perhaps, however, it would really be more consistent with the facts to regard it as composed of two parts: 1. The upper part, or petiole, generally provided with a leaf-blade; and 2. The base, which also is often provided with a pair of stipules. |