204 HISTOLOGY OP MEDICINAL PLANTS 



MOUNTAIN LAUREL 



Epidermis. The epidermal cells of mountain laurel are oc- 

 casionally modified, as unicellular hairs (Plate no. Fig. i), 

 particularly in the region of the veins. The ordinary epidermal 

 cells have thick outer walls and thin inner walls. Beneath 

 many of the epidermal cells are large air-spaces. 



Upper Palisade Parenchyma. The palisade parenchyma 

 vary from four to five layers. The inner palisade cells are 

 shorter and broader than the outer layer of cells. 



Parenchyma. The parenchyma cells (Fig. 4) are rounded 

 in form and they are arranged in the form of columns which are 

 one cell in thickness above, but two to three cells in thickness 

 near the under epidermis. Between each chain of cells is a 

 larger intercellular space (Fig. 6) . In a few of the cells are large 

 rosette crystals. 



Under Epidermis. The under epidermal cells are uniformly 

 smaller than the upper epidermal cells. 



It is thus seen that mountain laurel leaf has no hypodermal 

 cells; no spongy parenchyma; no under palisade cells; no under 

 hypodermal cells, and no secretion cavities. 



TRAILING ARBUTUS 



Epidermis. The epidermal cells of the trailing arbutus 

 (Plate in, Fig. 2) are variable in size. Many of the cells are 

 modified, as guard cells (Fig. i). 



Parenchyma. The parenchyma cells are round and they 

 are compactly arranged (Fig. 3) on the upper side of the leaf, 

 but on the under side they are arranged in round, small, intercel- 

 lular spaces (Fig. 5). In some of the intercellular spaces are 

 rosette crystals (Fig. 7). 



Under Epidermis. The under epidermal cells are smaller 

 than the upper epidermal cells. 



It will be seen that the structure of trailing arbutus leaf is 

 very simple and that its structure is different from that of klip 

 buchu and mountain laurel. 



The structure of powdered leaves is very variable, yet char- 

 acteristic for a given species. The leaves from the insect flower 

 plant are collected with the stems, and ground and sold as a 



