50 



ANATOMICAL STRUCTURE OF THE OLIVE. 



Fig. 16.— Ofle of the peltate hairs 

 from the surface of an olive leaf. 

 (X 150.) 



case seven years. Since in both cases the ground water was out of 

 reach of the roots and since the average yearly rainfall in Phoenix is 

 but 8.11 inches and at Palm Springs only 3.5 inches, it is evident that 

 these leaves were produced under extremely arid conditions. In fact, 

 the conditions at Palm Springs probably represent the extreme of 

 drought that the olive tree can endure. In both cases the varieties 

 were not identified. For purposes of comparison, similar material of 

 the Mission olive, the variety most widely grown in California, was 



obtained at Niles, Cal., where the trees are 

 irrigated at least once during the season 

 and where the average yearly rainfall is 

 14.8 inches, with a low evaporation due to 

 the cool summer climate. The leaf and 

 stem structure of the last, which may be 

 regarded as typical of Olea europea in the 

 western United States, is as follows: 



On the upjjer (ventral) face the cuticle 

 is smooth and thick; the lateral walls of 

 the epidermis cells, viewed superficially, 

 are straight and very much thickened; stomata are wanting and 

 peltate hairs (fig. 16) are scattered over the surface. On the lower 

 (dorsal) face the cuticle is similar; the radial walls of the epidermis 

 cells are almost straight, but not so much thickened as on the upper 

 face; the numerous stomata (fig. 17) are sunken, with narrow and 

 not very deep air chambers, and are surrounded by a variable 

 number of undifferentiated epidermis cells; peltate hairs (fig. 16) are 

 abundant, forming a continuous covering over the blade. The outer 

 walls of the epidermis cells (figs. 17 and 18) are very thick on both 

 faces of the leaf and show an increase in 

 thickening very plainly. On the dorsal 

 face they show many deepenings caused 

 by the irregular thickening of the cell 

 wall (fig. 17). The inner and radial cell 

 walls of the epidermis are rather thin as 

 compared with the outer walls. The 

 unicellular stalks of the lai-ge shield-shaped hairs are located in cir- 

 cular cavities, the peltate part of the hair, which consists of numerous 

 radially arranged cells, resting upon the outer wall of the epidermis. 

 The chlorenchyma is difi'erentiated into palisade and pneumatic 

 tissues. The former (fig. 18) consists of three compact layers of very 

 high cells containing chlorophyll and small needle-shaped crystals of 

 calcium oxalate. It extends from the margins of the blade to the 

 midril), where it ceases, being broken by the hypodermal collenchyma. 

 On the dorsal side of the blade there is a thick pneumatic tissue of 

 many layers. The cells which, like those of the palisade, contain 



eq... 



Fig. 17.— a sunken stoma and the un- 

 even dorsal surface of an olive leaf. 



