70 CARNEGIE INSTITUTION OF WASHINGTON. 



satisfactory manner than the weighing of pans of saturated soil under 

 laboratory conditions and with unnatural surface. 



In connection with the work on the physical properties of soils in 

 the Tucson region, determinations have been made on four of the 

 soil types under different conditions of moisture. On April 6, follow- 

 ing a rain of 0.56 inch, the following averages were secured, in 

 grams per square meter per hour: flood-plains 0.08, sandy outwashO.06, 

 outwash 0.05, playa 0.04. Another series of determinations made in 

 the same localities one week later found the flood-plain soil so dry that 

 no rise of the polymeter was registered in 20 minutes. The losses from 

 the other soils were: sandy outwash 0.02, outwash 0.03, playa 0.01. 



With accurate precipitation data, and with the determinations of 

 soil-moisture taken in connection with the readings of evaporation, 

 it becomes possible to follow with greater accuracy the history of the 

 water which falls on desert and other soils. The extreme difficulty 

 and uncertainty of measuring the run-off and also the amount of 

 water penetrating the soil to considerable depth makes it important 

 to be able to measure the remaining source of loss by physical agencies, 

 especially since this is the only one of the agencies that it is possible 

 to control in the agricultural management of soils. 



History of Groicth in a Monterey Pine as read from the Longitudinal Section 

 of the Trunk of a Full-grown Tree, by D. T. MacDougal, H. von Schrenk, 

 and Forrest Shreve. 



Early in July 1921, a tree of Pinus radiata, selected for size, age, 

 and location, of mature height but still showing excurrent growth, 

 was felled and the trunk cut away on one side of the central axis by a 

 skilled woodsman, so as to expose the pith in a median longitudinal 

 section of the entire trunk. The half log was then cut transversely 

 at intervals of 2 meters. With this material a detailed study has 

 been begun of all the geometrical features of growth in length and 

 diameter, of the relation between growth in diameter at various 

 levels from base to top, of the correlation between growth in height 

 and increase in diameter, of the features accompanying the attain- 

 ment of mature height, and of the relation between growth and the 

 local climatic conditions. The ease with which all measurements 

 and observations on the cross-sections can be checked and supple- 

 mented by reference to the longiloudinal surface gives an exceptional 

 opportunity to determine features of growth-behavior which are 

 usually inferred or interpolated from incomplete material. 



The tree was 20 meters in height and 40 years old, if a liberal allow- 

 ance of two years is made for the attainment of the stump height of 

 10 cm. After felling and determining the age of the tree, it was 

 found that the relation between its age and diameter is such as to 

 place it almost precisely in the mean of a curve of age-diameter rela- 



