44 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 



Series I. 



Station 7 is an altogether favorable spot for the study of the forest 

 soil. Station 10 was selected to represent the chaparral because it 

 was the only one having a soil in which it would be possible to 

 excavate to the desired depth. For the study of conditions surround- 

 ing the deep-rooted chaparral species, a knowledge of the water 

 conditions in the deeper soil-layers seemed essential. Even here the 

 deepest excavation possible did not approach the region reached by 

 the longest roots, which, as will be shown (p. 89), penetrate the 

 undecomposed sandstone to a considerably greater depth. Extreme 

 shallowness of soil is general over the chaparral area in which the 

 studies were made. It was felt that this advantage in depth of soil, 

 which station 10 possessed, compensated for certain disadvantages — 

 lack of slope contrast to station 7, the angle being only 7° southward, 

 and slightly disturbed condition, due to proximity to an old road 

 and the edge of the chaparral area. 



The series was begun January 21, 1913, and continued for a 

 total of 54 weekly observations, ending January 26, 1914. Occa- 

 sionally a visit was delayed for a day or two by storms or other 

 causes, especially in the winter of 1913-14; otherwise the program 

 was carried through without a single break or mishap of any kind. 

 Samples were taken in each station at three depths: 10, 50, and 100 

 cm. Excavations were made with a spade and samples were col- 

 lected in numbered and weighed glass bottles. The sample was 

 obtained, whenever conditions permitted, by pushing the mouth of 

 the bottle into the freshly exposed soil-surface. When this became 

 impossible toward the end of the dry season, especially at the lowest 

 level, lumps of soil were cut out and pressed into the bottle, which 

 was immediately tightly corked. The first weighings were always 

 made within a couple of hours after digging the samples and were 

 carried out to 0.01 gram, which is probably greater accuracy than is 

 necessary in such determinations. The soils were dried at a tem- 

 perature of 105° C, and the water-loss was computed upon the 

 basis of dry weight. 



The results have been plotted together in figure 8. The first 

 winter was a very dry one, the total precipitation at Palo Alto 

 being only 19.49 cm. Assuming a proportional relation at Jasper 

 Ridge, the rainfall at the latter locality should have been 32.5 cm. 

 The winter of 1913-14 was in great contrast to the preceding one, 

 the precipitation at Palo Alto being 62.15 cm. and at Jasper Ridge, 

 by actual measurement, 103.71 cm. 



Taking first the three curves representing the soils of station 10, 

 in the chaparral, we observe the following facts: The effect of 

 rainy and dry seasons is the most conspicuous feature. The highest 

 point reached in the first rainy season was 13 per cent, in the second 



