THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 105 



Vacdnium ovatum (fig. 39). — (2) Bifacial. Palisade tissue two layers in depth, occu- 

 pying one-third or less of the mesophyll, its cells very short and rounded; sponge very 

 loose. (3) Cells of upper epiderm large, with a moderately thick cuticle; lower cuticle 

 very tljin. (4) Stomata on lower side only, very slightly elevated. (5) Tannin in bundle 

 sheath and in the mesophyll, mainly the sponge-cells. 



Table 14. — Summary of structural characters. 



The principal structural characters of the species described are 

 summarized in table 14 by communities. From the data given, 

 we may characterize the average Californian broad-sclerophyll leaf 

 as follows: 



It is moderately small (averaging 2 to 3 cm. in length), simple, 

 unlobed, elliptic, and in a majority of cases entire and glabrous. 

 Important groups are toothed, spiny-toothed, revolute, or pubescent 

 on the lower or on both surfaces. The leaf is thick, averaging 

 314 microns, while the deciduous species studied average only 

 127 microns. The mesophyll is most commonly bifacial, though often 

 imperfectly so, but a few are isolateral. The palisade tissue is 



