THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 89 



The branching of the shrub species is notoriously close and intri- 

 cate, and the clump habit is almost universal, partly but not wholly 

 due to fire. Many of the tree species show a similar manner of 

 growth— several stems from a single base (often because of fire) — and 

 contorted assurgent or horizontal branches. Quercus agrifolia is a 

 notable instance, with its branches of enormous size frequently 

 resting on the ground. Most of the trees are marked by great 

 spread of branches rather than by height. A specimen of Quercus 

 agrifolia near Palo Alto shades an area 30 meters in diameter, and 

 this is not an extreme case. The deliquescent mode of branching 

 is the rule. Even when there is a distinct trunk, it is soon lost in 

 the branches. Pasania and Castanopsis exhibit the closest approach 

 to the excurrent type, maintaining a distinguishable trunk almost 

 throughout. Young specimens of Umbellularia show the same form 

 very perfectly, so that one frequently takes them at a distance to 

 be conifers. Large trees of this species are usually branched near 

 the base, but the separate stems maintain the excurrent form. 



This seems an appropriate place to mention the small but con- 

 spicuous group of species which have more or less spinescent branches. 

 These are Xylothermia montana, Ceanothus cordulatus, C. divaricatus, 



and C. incanus. 



ROOT SYSTEM. 



Somewhat scanty evidence indicates that the root systems of 

 the chaparral shrubs, when growing in loose soil, are prevailingly 

 of the "dual type" described by Cannon (19). Such root systems 

 are in part deeply penetrating and in part superficial, the latter 

 making up the greater bulk. Cannon states that the sclerophyll 

 Quercus agrifolia and the deciduous Q. douglasii and ALsculus cali- 

 fornica are of this type, and suggests that the deeply penetrating 

 roots, which may reach to the neighborhood of the water-table, 

 are formed in youth, while the more numerous superficial roots 

 are developed later. 



The root system of a large specimen of Adenostoma growing on 

 Jasper Ridge near Palo Alto was carefully excavated and charted 

 (fig. 19). This plant grew in a spot where the soil was pure sand, 

 gradually compacted downward into undecomposed sandstone. 

 It was impossible to trace the roots to a greater depth than a meter, 

 and this was the only locality on the ridge where excavation was 

 feasible at all. The plant grew close to station 10 of the habitat 

 study series. Its root system was decidedly of the dual type. 

 Figure 19 (lower), drawn as if the roots grew all in one plane, exhibits 

 their vertical distribution. It is very common for a large root, at 

 first horizontal, to bend suddenly downward. Several such, lost at a 

 depth of a meter, were 6 to 7 mm. thick at that point. No tap-root 

 or anything approaching it was found, though every seedling possesses 



