THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 41 



supplied with humus therefrom. The occasional rock outcrops 

 bear a fair amount of moss vegetation. 



Station 8. 



This is similar to the last, but is close to the ravine bottom. 

 Umbellularia californica is very important, growing in dense groups, 

 which cast almost complete shade. Lower vegetation is almost 

 absent in such places (although a healthy seedling of Umbellularia 

 was found), but elsewhere the herbaceous element is like that 

 described above. 



Station 9. 



A sudden change of habitat, due to the sharp V-shaped bottom 

 of the ravine, brings about a transition in vegetation that is even 

 more abrupt than that between stations 3 and 4. Facing the 

 oak-madrono slope and beginning in full development at the very 

 bottom of the ravine, we find a nearly pure growth of Adenostoma. 

 The shrubs are larger here than in any previous station dominated 

 by that species, averaging 1.5 meters in height. The living and 

 dead branches are so densely interlaced that progress even on hands 

 and knees is almost impossible. The following summary of the 

 quadrat (fig. 7) gives a satisfactory picture of the composition: 



Clumps. Sterna. 



Adenostoma 29 175 



Ceanothus sorediatus 1 I 



Total 30 176 



The one specimen of Ceanothus sorediatus overtops everything 

 else. The shade is dense, considering the fact that Adenostoma is 

 responsible for most of it. Ground-cover is very sparse and consists 

 of Aster radulinus, Chlorogalum pomeridianum, and occasional small 

 plants of Diplacus glutinosus. Litter and humus are scanty and 

 the steep slope shows frequent rock outcrops. 



Station 10. 



This is situated on the gently south-facing slope, 130 meters south 

 of the last. It was chosen for special study because it was in the 

 only chaparral area where the soil was such that excavation for 

 water-content determination could be made in it to the desired 

 depth. The fact that the vegetation has been slightly disturbed in 

 consequence of its proximity to an old road does not vitiate its 

 usefulness for this purpose. Adenostoma is dominant and large. 

 Arctostaphylos and Quercus duraia are both frequent, and Q. wislizeni, 

 Heteromeles, and Prunus ilicifolia also occur. Because of disturbance, 

 Eriodictyon californicum, Helianthemum scoparium, and Diplacus 

 glutinosus are frequent, with quite an assemblage of small wet- 

 season annuals. Litter and humus are scarce. The uniform sandy 

 soil grades evenly into the bed rock, becoming too hard for excavation 

 at a depth of a little more than a meter. 



