46 



THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 



thus approaching a condition of constancy. The sudden rise with 

 the first autumn rain is the most striking single feature. Comparing 

 the three lines, we see that the 100 cm. level had the highest water- 

 content through most of the year, and the 10 cm. level the least. 

 The order was suddenly reversed immediately after rains, the 

 most striking case being at the beginning of the rainy season of 

 1913-14. The first rain occurred on October 31, and was a sudden, 

 heavy shower, followed by others at frequent intervals during the 

 month of November. From October 31 to November 6, inclusive, 

 the precipitation at Palo Alto was 3.5 cm. Figure 8 shows that on 

 November 7 the water-content at 10 cm. depth had risen from 0.5 

 per cent to 5.2 per cent and on November 14 to 10.2 per cent. 



The lag in the response of the lower levels is interesting. At 

 50 cm. depth no effect was observable until November 22, and the 

 increase when it came was less sudden. The water had not reached 

 100 cm. depth on December 5 and the rise thereafter was still more 

 gradual. The slow penetration of the rain-water is not due to 

 run-off, since the slope is only 7 per cent, but doubtless, in the main, 

 to the air-filled condition of the soil. Table 5 shows roughly the rate 

 of penetration in the two stations during this period. No important 

 difference between the two stations is seen in this respect, and the rate 

 of penetration was approximately uniform as far as it was followed 



Table 5. — Rate of penetration of first rains. 



Returning to station 10, we note further the tendency toward 

 convergence of the three lines as the dry season progresses. The 

 sudden jumps of July 13 and August 31 in the 100-cm. line are 

 difficult to explain. They may possibly be due to encountering 

 small masses of soil where the clay-content was above the average. 



We may draw the following conclusions concerning the soil- 

 moisture conditions in this particular chaparral station during the 

 period studied. During the actual continuance of the rainy season 

 there is an abundance of water at all depths. This was true even 

 in the unusually dry winter of 1912-13. As to the following very 

 wet season, the soil at station 10 was frequently so thoroughly 

 saturated that the walls of the excavations continually collapsed 

 into an almost soupy mass, making it difficult to obtain fair samples 



