70 



Elementary Botany 



In very many cases, however, there are only one or two of 

 these parts present. If the petiole be absent, the leaf is said 

 to be sessile ; if the stipules, exstipulate. 



The Wallflower and Shepherd's-purse (fig. 102) are ex- 

 amples of plants with leaves which consist of lamina only. In 

 some of the leaves of the Australian Acacias (fig. 103), we have 

 only the petiole developed. It grows in a flattened leaf-like 

 expansion know as a phyllode (fig. 103, a, b). 



Fig. 103. — Leaf of Acacia melanoxylont showing phyllodes «, b. 



In the Lathy rus Aphaca (fig. 104) the stipules are the only 

 parts which are developed in a leaf-like manner, the lamina 

 and petiole being converted into a tendril. 



In structure the leaf consists of parenchyma, which is in- 

 timately connected with the outer parenchyma of the stem, 

 and prosenchyma forming the veins, and which is in like 

 manner connected with the xylem and phloem. 



In a vertical section through the leaf we find the following 

 parts (fig. 105) :— 



