100 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 



Quercus chrysolepis. — The specimens are from the shrubby chaparral form. Even so, 

 they exhibit less of xerophytic character than the last, in that they are more perfectly 

 bifacial and that the sponge is more typical. Otherwise they are essentially like those of 

 Q. agrifolia. 



Pasania de>mflora.—(2) Bifacial. Palisade tissue about two layers in depth, occupy- 

 ing less than half the mesophyll; sponge not abundant, most of the space being taken up 

 by groups of large, thin-walled parenchyma cells, apparently water-storage tissue. (3) A 

 complete layer of hypoderm beneath the upper epiderm and resembling it; lower epiderm 

 papillate. (4) Stomata on lower side only. (5) Struts of mechanical tissue like those of 

 the other members of the family. 



Umbellularia calif ornica (fig. 24).— (2) Imperfectly bifacial. Palisade tissue two layers 

 in depth, occupying half the mesophyll, and an imperfect layer next to the lower epiderm; 

 large oil-cells in both palisade and sponge, many of those on the lower side being enlarged 

 elements of the epiderm (84, p. 703). (4) Stomata on lower side only. 



Arbutus menziesii (fig. 25). — (2) Bifacial. Palisade tissue of two complete rows, occu- 

 pying^one-third orjmore of the mesophyll. (3) Lower epiderm minutely papillate. (4) 

 Stomata on lower 'side only, with small exterior chamber formed by a collar-like ridge. 

 (5) Tannin very abundant, almost throughout the mesophyll. 



Fig. 27. — Dendromecon rigidum: section of leaf. 

 Fio. 28. — Dendromecon rigidum: stoma. X375. 



Climax Chaparral. 



Quercus durata (fig. 26).— (2) Imperfectly bifacial. Palisade tissue about three layers 

 deep, making half the mesophyll; sponge rather loose, but cells palisade-like. (3) Lower 

 epiderm papillate. (4) Stomata on lower side only. (5) Tannin in lower epiderm and to 

 some extent in upper; struts of mechanical tissue as in Q. agrifolia. 



Berberis pinnata.—(2) Completely bifacial. Palisade tissue two layers deep, occupying 

 half the mesophyll; sponge fairly typical. (4) Stomata on lower side only. (5) Struts 

 of mechanical tissue associated with veins. 



Dendromecon rigidum (figs. 27, 28).— (2) Almost perfectly isolateral, in correlation with 

 its vertical placement. Palisade tissue on both sides of leaf, two perfect rows above, two 

 imperfect ones below, rather loose; sponge central, occupying one-third of the mesophyll, 

 loose. (3) Both upper and lower epiderm strikingly papillate. (4) Stomata numerous 

 and large, on both surfaces, sunken in pits to the depth of the thickness of the epiderm. 

 (5) Struts of mechanical tissue associated with veins. 



Heteromeles arbutifolia.—{2) Bifacial. Palisade tissue about three layers deep, making 

 less than half the mesophyll; sponge abundant, rather typical. (3) Lower epiderm papil- 



