412 JOURNAL OF THE RO^L HORTICULTURAL SOCIETY. 



The normal number of stipules w!l be two to each leaf. Consequently 

 four would occur with opposite leaves ; hut the stipular zone is capable of 

 supplying additional ones ; so that the narubers of the tribe Stellatae 

 of Rubiaccae sometimes have more than foir so-called "leaves" at a 

 node ; for the stipules assume the same form aid size as the two true 

 leaves, but these only can produce buds in their \xils, and the leaves 

 can be recognized by their presence. 



The order Valerianaceae, allied to Bubiaceae, is exstipulate ; but 

 Gentranthus ruber, the "red valerian," which has established itself on 

 walls, &c, has the stipular zone and several branches proceeding 

 from it ; but they do not reach the surface. Hence it wouii seem to 



Fig. 79.— Transversa; Section of Petiole of Plane, showing how it surrounds 

 the Bum The upper Figure shows the Leaf just removed from the Shoot. 



indicate that the order is descended from a stipulate one, but nothing 

 now remains but the rudimentary fibro- vascular cords, the external 

 stipules being totally arrested. 



When the petiole sheathes the stem, as in Polygonwn, numerous 

 bundles may be given oft" from the sheathing stipule, as seen in species 

 of this genus ; even without sheathing many separate fibres may enter 

 a stipule, as in the pansy, all arising from the outermost leaf-bundle. 



Modifications of Parts of Leaves. — As the summer declines the winter 

 buds are formed in tho axils of the leaves. Though the outer parts of the 

 bud protect the inner, the leaf itself also provides for the protection of ity 

 bud. This is often done by the base of the petiole. Sometimes the base 

 of tht; loaf-stalk merely thickens around the bud, burying it, as it were. 



