62 



HISTOLOGY OF MEDICINAL PLANTS 



than have the leaves of plants growing in soil under normal 

 conditions, or than have the leaves of shrubs and trees. 



The widest possible range of cell-wall thickness is therefore 

 found in the medicinal leaves, because the medicinal leaves are 

 collected from aquatic plants, herbs, shrubs, trees, etc. 



The outer wall is always thicker than the side walls. Even 

 the side walls van- in thickness in some leaves, the waU next 

 to the epidermis being thicker than the lower or innermost 

 portion of the wall. Frequent!}- the outermost part of the side 

 walls is unequally thickened. This is the case in the beaded 

 side walls characteristic of the epidermis of the leaves of laurus, 

 myrcia. boldus. and capsicum seed. etc. The thickness of the 

 side walls of the epidermal cells of most leaves varies in the 

 different leaves. 



In most leaves there are five typical forms of arrangement of 

 epidermal calls: First, those over the veins which are elongated 

 in the direction of the length of the leaf; and. secondly, those 

 on other parts of the leaf which are usually several-sided and 

 not elongated in any one direction. If the epidermis of the leaf 

 has stoma, then there is a third type of arrangement of the 

 epidermal cells around the stoma; fourthly, the cells surrounding 

 the base of hairs; and fifthly, outgrowths of the epidermis, 

 non-glandular and glandular hairs, etc. 



It should be borne in mind that in each species of plant the 

 five types of arrangement are characteristic for the species. 



The character of the outer wall of the epidermal cells differs 

 greatly in different plants. In most cases the wall is smooth; 

 senna is an example of such leaves. In certain other leaves the 

 wall is rough, the roughness being in the form of striatioiis. 

 In some cases the striatioiis occur in a regular manner; bella- 

 donna leaf is typical of such leaves. In other instances the wall 

 is striated in an irregular manner as shown hi cliirata epidermis. 

 Very often an epidermis is rough, but the roughness is not due 

 to striatioiis. In these cases the epidermis is unevenly thickened, 

 the thin places appearing as slight depressions, the thick places 

 &s slight elevations. Boldus has a rough, but not a striated 

 surface. 



Surface deposits are not of common occurrence in medicinal 

 plants; waxy deposits occur on the stem of sumac, on a species 



