264 HISTOLOGY OF MEDICINAL PLANTS 
MOUNTAIN LAUREL 
Epidermis. The epidermal cells of mountain laurel are oc- 
casionally modified, as unicellular hairs (Plate 110, Fig. 1), 
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 111, Fig. 2) are variable in size. Many of the cells are 
modified, as guard cells (Fig. 1). 
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 
