i68 
PHARMACEUTICAL BOTANY 
This is most commonly the rule, but when the plant is exposed to 
xerophytic conditions, as the Acacias of 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. 
The petiolar structure in primitive types of Dicotyls resembles 
that seen in Monocotyls except that the bundles are more con¬ 
densed side by side. In these the petiole is somewhat dorsiventral, 
shows an external epidermis, a flattened cortex with a set of parallel 
vascular bundles, each with xylem uppermost and phloem below. 
From this we pass to another group in which the bundles form 
three-fourths of a circle and in which the upper bundles show incurv¬ 
ing orientation, to still another in which, as in Nepenthes , all of the 
bundles form nearly a cylinder. Finally in Ficus, Geranium, Podo¬ 
phyllum and other plants showing conpletely formed cylindric 
petioles, the bundles form a continuous ring enclosing pith and sur¬ 
rounded by cortex and epidermis, as in Dicotyl stems. 
Stipules.—Stipules are lateral leafy or membranous outgrowths 
from the base of the petiole at its junction with the stem. They 
may be divided into two groups, viz.: lateral and axillary. The 
lateral group includes four types, namely, free lateral, lateral adnate, 
lateral connate and lateral interpetiolar. 
Free lateral stipules are seen in Leguminosce, Rosacece, Beeches, 
etc. They are free on either side of the petiole and supplied by 
vascular tissue from the petiolar bundle mass. In appearance and 
duration they may be either green, foliaceous and persistent or mem¬ 
branous to leathery, scale-like and caducous. Caducous scaly stip¬ 
ules only function as bud scales through the winter and fall in spring 
as the buds expand. 
Lateral adnate stipules are such as fuse with and are carried up 
with the petiole as wing-like appendages. This type is seen in the 
genus Rosa, in Clovers, etc. 
Lateral connate stipules are such as join and run up with the 
petiole to form a structure which is called a ligule. This structure 
is common to the Gramineae or Grass family. 
Lateral interpetiolar stipules are common to many species of the 
Rubiacece. In the genus Cinchona the leaves are opposite and orig- 
