92 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 



are most abundant naturally in the upper soil layers, where there is 

 most humus. Pockets of nearly pure humus were occasionally 

 found, probably derived from rotted roots, which were thoroughly 

 penetrated by the coralloid rootlets. The mycorhizas were by no 

 means confined to the regions of abundant humus, however. The 

 roots which penetrated the pure sand below the humus layer were 

 almost as well supplied with the fungi. In station 2, where the soil 

 is m.erely a slightly decomposed clayey sandstone, well-developed 

 mycorhizal roots of Ardostaphylos were taken from tight crevices 

 between the fragments. 



The best material for study was obtained from Quercus durata. 

 The last few centimeters of the roots were found to branch freely, 

 giving off numerous clumps of blunt-tipped coralloid rootlets, each 

 clump firmly embedded in a mass of sand-grains bound together by a 

 network of fungal hyphse. The hyphae were of two kinds: (1) very 

 small, transparent, branched, quite certainly non-septate, much 

 more abundant than (2), doing most of the sand-binding; (2) diameter 

 twice or thrice that of (1), branched, very dark brown, some opaque, 

 others only partially so, plainly septate. What appeared to be 

 tight bundles of hyphse of the septate type were seen, simulating 

 rootlets. A cross-section of a mycorhizal root of this species is 

 given in plate 20a. The dense felt of mycelium completely sheathing 

 the root is well shown, and the hyphae are seen to penetrate between 

 the cells of the cortex, so that some of the outer ones are apparently 

 isolated from their neighbors. The strands which originally extended 

 out into the soil have, of course, been lost in the process of slide- 

 making. 



THE LEAF. 

 THE DECIDUOUS ELEMENT. 



Of the 91 species listed on pages 113 to 120 as being included in the 

 broad-sclerophyll communities as dominants, 18 or 19.8 per cent 

 are deciduous. These are as follows (two or three species which lose 

 their leaves in late winter or spring are classed as evergreens) : 



Corylus rostrata californica.* Amelanchier alnifolia.* Acer macrophyllum.* 



Quercus breweri. Prunua demissa.* iEsculus californica. 



douglasii. emaiginata.* Ceanothus integerrimus. 



garryana.* subcordata. parryi. 



kelloggii. Cercis oceidentalis. parvifolius. 



lobata. Acer glabrum.* sanguineus.* 



Omitting those which are not characteristically Californian 

 (marked by asterisk), the number is reduced to 10, or 11 per cent. 

 The relation of the evergreen habit to the Californian habitat is 

 further shown by a comparison of the three communities. The 

 climax chaparral, most characteristically Californian, with a total 

 of 44 dominant species, has no deciduous dominants, the broad- 

 sclerophyll forest, with the small total of 13, has 4 deciduous, or 



