Sas i a 
244 PHARMACEUTICAL BOTANY 
plant is exposed to xerophytic conditions, as the Acacias of 
Africa and Australia, the stalk, instead of being cylindric or sub- 
cylindric, becomes flattened from side to side, until there is 
produced a bifacial, vertically placed petiole, with a large green 
surface that wholly takes the place of the lamina. Such a 
structure is known as a PHyLLope or PHyLiopium. (Fig. 165.) 
Stoma 
Fic. 165.—A Phyllode, or Blade-like Petiole, from Acacia melanoxylon, and its 
Cross-Section. Drawing by H. McCarthy. (After Stanford, General and Economic 
Botany, D. Appleton-Century Co. publishers.) 
The INTERNAL STRUCTURE OF THE PETIOLE in primitive types 
of Dicotyledons resembles that seen in Monocotyledons except 
that the bundles are more condensed side by side. In these the 
petiole is somewhat flattened and shows an external epidermis, a 
flattened cortex and a single row of vascular bundles, each with 
xylem uppermost and phloem below. From this we can pass to 
another group of these plants in which the bundles form three- 
fourths of a circle and in which the upper bundles show incurving 
