392 CARNEGIE INSTITUTION OF WASHINGTON. 



ignore photosynthesis and respiration, as these basic processes in- 

 fluence each other mutually. 



During the summer the sap-content of the trunks and leaves and 

 the stomatal behavior of woody plants was investigated at the Alpine 

 Laboratory, while the absorption, conduction, transpiration, and 

 stomatal changes of several native and cultivated herbs were followed 

 at the Desert Laboratory. In the former, an endeavor was made to 

 correlate the amount of water in the leaves and wood of several coni- 

 ferous and deciduous trees and shrubs with transpiration and stomatal 

 movement, and to relate these to the physical factors concerned. In 

 the case of Pinus ponderosa and Pseudotsuga mucronata the sap- 

 content of the trunk stood in close relation to that of the leaves, 

 and the fluctuations shown by the dendrograph coincided with its 

 changes. No such close relation could be established in the case of 

 the deciduous shrubs, owing to the great variation in the sap-content 

 of the branches. 



Relation of Bud to Trunk-Growth in Conifers, by J. V. G. Loftfield. 



Dendrographs were again installed in the spring on the trunks of 

 Picea engehnanni, Pseudotsuga mucronata, and Pinus ponderosa, in 

 cooperation with Dr. MacDougal. The increase in the length of buds 

 and needles was recorded at weekly intervals and plotted in comparison 

 with the change in the nightly maximum of the trunk. The buds of 

 all three started to grow on the same date, June 2, but those of Picea 

 completed their growth first, followed by those of Pseudotsuga, and 

 later by those of Pinus. The trunks of the first two began to grow 

 simultaneouslj^ with the buds, but the trunk of Pinus did not show 

 growth until two weeks later. Growth was very slow during the lat- 

 ter part of July, and had practically ceased by the end. 



An explanation of this behavior was sought in the rate at which 

 heat penetrated the trunk. Thermometers reading to 0.1" C. were 

 inserted 3 cm. deep in the trunks, and observed daily at 2 p. m. and 

 at 2-hour intervals for 3-day periods at various times. It was found 

 that the temperature of Picea fluctuated most nearly like that of the 

 air, and that of Pseudotsuga least nearly. With respect to the rise of 

 temperature with the afternoon sun, the spruce usually showed a de- 

 cided increase in 1 hour, pine in 2, and Douglas fir in 2.5 hours, the 

 rate corresponding approximately with the thickness of the bark. 



The Significance of Transpiring Power, by R. J. Pool. 



An investigation has been undertaken to determine whether there 

 is any regular correlation between the leaf structure of plains plants 

 and the so-called transpiring power, as indicated by the refined cobalt- 

 paper method. Many species have been studied in the field in a wide 

 range of habitats by this method, and abundant material has been col- 



