44 The Nature and Origin of Stipules. 



much more extensive and is reenforced by several small branches 

 from the latei'al bundle which enters the petiole, below the main 

 stipular branch. This additional supply of vascular tissue is evi- 

 dently rendered necessary by the exposure of the stipules to the 

 light and air and the development of chlorophyll. It seems to be 

 of secondary introduction. 



The nearest approach to the stipular conditions occurring in 

 Fragaria and Rosa which I have observed among the Legumi- 

 nosse is found in the adnate stipules of Trifolium pratense 

 L. (fig. 10). There are two sets of stipular bundles. One of 

 these supplies the tip of the stipule and consists of three veins of 

 which the lowest corresponds to the single large bundle of the 

 tip of the stipules of Fragaria and Rosa. The other has its ori- 

 gin as branches from the lateral bundle of the leaf-trace at the 

 base of the leaf, the usual point of origin of the veins of free stip- 

 ules. This set of veins is distributed to the lateral and basal 

 parts of the stipules and apparently corresponds to the lower net- 

 work of the stipules in Fragaria. These stipules are mainly 

 protective in function. Their meshes are filled with hyaline tis- 

 sue, but there is some green parenchyma along the veins. 



Two very interesting cases in the family of the Rosacese are 

 those of Gliffortia graminea L. f. of South Africa ( fig. 71 )and 

 Potentilla fruticosa L. ( fig. 72 ). In the former the leaves very 

 closely simulate those of grasses with the linear lamina sessile 

 upon a sheathing petiole. They differ in having the tips of the 

 lateral portions ( stipules ) free instead of turning in across the 

 insertion of the lamina to form a ligule. In the latter the con- 

 ditions are very closely similar to those of the ochrea of Polygo- 

 num. There is a short sheathing petiole, above the apex of which 

 the tips of the stipules rise. Each of them is supported by a 

 strong vein which has its origin at the base of the true petiole. 

 But instead of being free from one another as in Rosa, the stip- 

 ules are connected back of the petiole by a hyaline ligular tissue. 

 The lateral portions of the sheathing petiole are also united to 

 one another on the opposite side of the stem, at least in young 

 leaves, to a considerable degree. Thus an ochrea is formed, not 

 quite a typical one it is true, yet more nearly so than that of 

 Polygonum sagittatum L. ( fig. 32 ). 



The fact that such forms as these can occur in the same family 

 of plants along with typical stipules, both adnate and free, goes to 



