88 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 



VI. ECOLOGICAL CHARACTER OF THE BROAD-SCLERO- 

 PHYLL SHRUBS AND TREES. 



As a text for this chapter I will quote a paragraph from the pioneer 

 of physiological plant geography. He is characterizing the broad- 

 sclerophyll type in general (80, p. 510). 



"The trees are usually low, their stems generally massive, and the branches 

 gnarled. The leaves are at most of moderate size, about as large as the leaves of 

 laurel or oleander, usually smaller, or even very small; they are scarcely ever com- 

 pound, as a rule narrow, lanceolate or linear to acicular; their margins are usually 

 entire. The leaves are not generally placed with their flat surfaces perpendicular to 

 the strongest light, but usually avoid it by assuming an oblique or parallel position. 

 They are either destitute of an air-containing tomentum, or this is confined to their 

 under-surface; on the other hand glandular hairs are not uncommon on both leaf- 

 surfaces. Even when there is no tomentum the leaves comparatively speaking are 

 seldom shiny, but more frequently, even if smooth on the surface, are dull, perhaps 

 owing to exudations of resin, and often bluish. Histologically the foliage is character- 

 ized by the thickness of the walls of all the cells, including even the parenchymatous 

 ones, by the abundance of sclerenchyma, by the strong development of cuticle, and 

 by the diminution of the intercellular spaces; these qualities in the aggregate give the 

 leaf its characteristic, stiff, leathery consistency." 



In the large, this is an adequate brief characterization of the 

 California broad-sclerophylls. The following detailed analysis will 

 confirm Schimper's statements in the main, at the same time pointing 

 out features in which the California species diverge from his generali- 

 zations. 



GROWTH FORM. 



A very great majority of the California broad-sclerophylls (88 

 per cent) are shrubs. In Raunkiar's scheme (83) they would be 

 classed as nanophanerophytes. The height of mature individuals 

 is naturally variable. Adenostoma may be found, under various 

 conditions, 3 dm. high to 4 meters high. The average for all shrubby 

 species, for the region as a whole, may fairly be placed between 

 1.5 and 2 meters. In a single locality the height of the individuals 

 of all species is usually remarkably uniform. A few species, which 

 do not usually occur in abundance, habitually rise above their 

 neighbors. Such are Heteromeles arbutifolia and Garry a elliptica 

 and those which are potential trees. The broad-sclerophyll trees 

 come mainly under Raunkiar's class of mesophanerophytes (8 to 30 

 meters). Castanopsis occasionally attains a greater height, and 

 probably Pasania and Arbutus also. Most of the trees reach great 

 size under favorable conditions. The diameters of the largest speci- 

 mens that I have measured are as follows: Quercus agrifolia, 2.1 

 meters; Quercus chrysolepis, 1.8 meters; Arbutus menziesii, 1.5 meters. 

 Greater diameters have been reported for these species, and Sargent 

 (79) reports 3 meters as the maximum for Castanopsis, 1.8 meters 

 for Pasania, and 1.5 meters for Unibellularia. 



