1 68 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 Leguminoscz, 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 Graminese or Grass family. 



Lateral interpetiolar stipules are common to many species of the 

 Rubiacea. In the genus Cinchona the leaves are opposite and orig- 



