" 3. The axillary region, which unites the two stipular regions, a lamina, usually of parenchyma, but which may receive bundles arising from the internal doubling of those bundles of the sheath which become petiolar.
" The sheath may be reduced even to complete disappearance without a consequent disappearance of the lignle.
" 1. If the ligule is complete with its three regions, I give it the name of an axillary ligule.
" 2. If the stipular and axillary regions only persist, the sheath ing regions having disappeared, we have an axillary stipule.
" 3. If finally the axillary region divides into two halves, right and left (which would not be remarkable, considering its purely parenchymatous nature), the stipular regions exist alone at the base of the petiole, and we have then stipules properly so-called.
" Stipules and the ligule are then organs of the same nature, between which it is possible to find all forms of intergradation, the stipule being a portion of the axillary ligule.
" When, finally, the manner of origin of the bundles of the stipule is studied, we arrive at the following definition of the organ: An appendage inserted on the stem, at the base of the leaf, all the bundles of which arise exclusively from the corresponding foliar bundles." Each of the tendrils of a leaf of Smilax is characterized as a demi-ligule, the " stipule " of Potamogeton as a ligule identical with that of grasses, the ochrea of Polygonum and Platanus as axillary stipules, the stipules of Ficus elastica Roxb. and Magnolia grandi.. flora L. as axillary ligules.
Professor Ward says (p. 41) in speaking of the fossil leaves of Platanus basilobata Ward, of the Yellowstone valley, that some of those found had "a remarkable expansion at the base of the blade, projecting backward on the leaf-stalk and having two to five lobes or points.
" These expansions are to be interpreted as evidence that the leaves all belong to Platanus or to some extinct ancestral type of the genus, since something quite analagous to them is found in our American plane-tree. The ordinary leaves of this tree are, it is true, destitute of basilar expansions, but those on young shoots, and sometimes those on the lower or non-fruit-bearing branches of trees exhibit this peculiarity.
leaf from a young shoot of Platanus corresponding to the fossil form of Platanus appendiculata Lesq. from the auriferous gravels of California. The indication is that "the constriction seen in the fossil forms between the blade of the leaf and the appendage would seem to represent the beginning of this process of detach ment." Ward, L. of the Plane-Trees. Am. Nat. 24: 797-910. 1990. The same cases as those in the preceding paper are discussed, the appendages in Platanus appendiculata Lesq. being described as stipular, while those of P. nubilis Newb. and P. basilobata Ward arc not so considered.
" The primary function of stipules seems to be to protect the bud. In other species, however, they serve as accessory or deputy leaves. Their protective function is confirmed by the fact of their early fall. Some are more persistent than the leaves and protect the leaves of the following year.
" When stipules are present [in Helianthemum] the petiole is always very narrow, semiterete, and tapered to the base. Where they are absent the leaf is often sessile and, whether or not, its base is always dilated and concave on the inner face, completely enclosing the bud up to a certain stage of its development." The presence of stipules in the lower imperfect leaves of Ailan thus glandulosa Desf. is noticed, though the family of the Sim arubiacem has been described as exstipulate. In Ribes sanguin eum Pursh. the bud-scales are described as consisting of the dilated base of the petiole, the lamina being represented by a. small black point. " One or two succeeding leaves bear a small lamina sessile on the sheath, which is wholly adnate to the thin dilated base of the petiole and membranous, especially outside of the three vascular bundles. The next one or two have a well developed lamina., and the sheaths partly separated from the petiole and corresponding to stipules. Farther up the stipular sheaths are shorter and wholly adnate to the petiole." The form and function of the stipules in a large number of species are described.