96 



FORMS OF PETIOLES OE LEAF-STALKS. 



lemon and Dionsea (fig. 202 p). In some Australian Acacias, and in 

 some species of Oxalis, Bupleurum, etc., the petiole is flattened in a 

 vertical direction, the vascular bundles separating immediately after 

 quitting the stem, and running nearly parallel from base to apex. 

 This kind of petiole (fig. 204 p) has been called Phyllodiwm {(pdXKov, 

 a leaf, and l/Sos, form). In these plants the laminae or blades of the 

 leaves are pinnate, bipinnate, or ternate, and are produced at the 

 extremities of the phyllodia in a horizontal direction (fig. 204 I) ; but 



"Fig. 202. 



Fig. 203. 



Fig. 204. 



in many instances they are not developed, and the phyUodium serves 

 the purpose of a leaf. Hence some Acacias are called leafless. 

 These phyUodia, by their vertical position and their peculiar form, 

 give a remarkable aspect to vegetation. On the same Acacia, there 

 occur leaves with the petiole and lamina perfect ; others having the 

 petiole slightly expanded or winged, and the lamina imperfectly 

 developed ; and others in which there is no lamina, and the petiole 

 becomes large and broad. Some petioles, in place of ending in a 



Fig. 202. Leaf of Dion^a nmscipula, or Venus' Fly-trap, y, Dilated or winged petiole. 

 e. Jointed blade, the two fringed halves of which fold on each other, when certain hairs on 

 the upper siuface are touched. Fig. 203. Ascidium, or Pitcher of Sarracenia, formed by 

 the petiole of the leaf. The lid is not articulated to the pitcher as in Nepenthes (fig. 200). 

 Fig. 204. Leaf of Acacia heterophylla. p, PhyUodium or enlarged petiole, with straight 

 venation. 1 1, Lamina or blade, which is bipinnate. The blade is frequently wanting, and 

 the phyUodium is the only part produced. 



