52 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 



volume. The method employed was the one which has been in 

 general use of late. Circular pans were made having bottoms of 

 perforated metal, with sides 1 cm. high and of such an area that the 

 capacity, when the soil was smoothed off level with the top, would 

 be 100 c. c. The bottoms were covered with cheese-cloth. The soils 

 were all prepared — pulverized and compacted — as nearly as possible 

 in the same way, and the pans, filled level full, were stood in shallow 

 water to permit absorption. After saturation was complete they 

 were allowed to drain until all the gravity water had passed off. 

 The percentage of water retained was then calculated upon the 

 basis of dry weight and also of dry volume. In each case the average 

 of five tests was used. The shortcomings of the method are fully 

 realized, prominent among them being the unnatural condition of 

 the soils when tested. The results, however, although they do not 

 give a true picture of the behavior of a given soil under natural 

 conditions, do give data whereby fair comparison may be made 

 between different ones. Samples were taken from the three depths 

 in stations 7 and 10 for comparison of conditions in forest and 

 chaparral, and from station 2 because of its peculiar qualities. 



Table 7. — Water-retaining capacity, percentages. 



Considering the dry-volume figures, which give the truest picture 

 of the soil qualities, we note that there are no differences of im- 

 portance among the various depths in station 10. The high water- 

 retaining capacity in station 7 at 10 cm. depth is plainly due to the 

 large humus content. The high figure for station 7, 50 cm. depth, 

 as compared with the low one for 100 cm., is difficult to explain. 

 Mechanical analysis offers no clue; nor does humus content, since 

 50 cm. and 100 cm. are more like to each other than to 10 cm. depth. 

 Station 2 shows striking originality in this feature as in others, and 

 the reason is plain — the high percentage of clay and silt. Sum- 

 marizing, we find that the comparative water-retaining capacities 

 of stations 10, 7, and 2, repre.senting chaparral, forest, and a par- 

 ticularly unfavorable chaparral station, may be expressed by the 

 ratio 1 : 1.13 : 1.87. 



