LABORATORY FOR PLANT PHYSIOLOGY. 45 



where both rose or fell together. Out of 19 years, in only 5 years were all 

 6 of the trees in agreement inter se and with the rainfall. In one year the 

 trees were all in agreement, but did not agree with the rainfall. There were 

 only three additional years in which 5 of the 6 trees were in agreement. 

 Out of 108 possible agreements for the 6 trees, there were only 68 actual 

 agreements, indicating a percentage correlation of 62.9. In the case of the 

 4 large trees this percentage was 50.9. These figures indicate a very weak 

 influence of rain upon growth in young trees, and none in mature trees. A 

 comparison has been made of the growth of the above-mentioned trees in 

 the four wettest and the two driest years in the last 25 years. For the small 

 trees the average wood increment in the wet years was 4.3 mm., in the dry 

 years 2.6 mm., but in the large trees the increments were 6.1 mm. in the wet 

 years and 7.6 mm. in the dry years. The amounts of growth per inch of 

 rainfall in the small trees are about twice as great in the dry years as in the 

 wet, and in the large trees nearly four times as great in the dry years as in the 

 wet. This indicates that, whatever qualitative correlation there may be 

 between growth and rainfall, there is a pronounced lack of any quantitative 

 relation between the amount of growth and the amount of rain in a given 

 year. 



In the years 1912 and 1921 the seasonal rainfall was nearly the same 

 (13.38 inches and 13.97 inches, respectively). The average amounts of 

 growth in the two years were 3.2 mm. and 2.6 mm., respectively, for the small 

 trees and 4.22 mm. and 4.30 mm. for the large trees. In order to evaluate the 

 influence of temperature on growth in these years with nearly the same rain- 

 fall, summations of all temperatures above 40° F. were made, covering the 

 months of active growth (January to April) and the entire growing-season 

 (January to September), and based on the thermograph records taken at the 

 Coastal Laboratory. For the period of active growth the totals are 28,253 

 hour-degrees for 1912 and 30,261 hour-degrees for 1921. For the growing 

 season the figures are 92,950 hour-degrees for 1912 and 94,969 hour-degrees 

 for 1921. These small differences between the two years are in agreement 

 with the very small difference between the growth of the 4 large trees and in 

 disagreement with the amounts of growth in the 6 young trees. These 

 preliminary data afford some evidence that rainfall is of greater importance 

 than temperature in the growth of young trees, and that temperature is of 

 greater importance than rainfall in the case of mature trees. It is at least 

 apparent that in the Monterey pine, growing in its native coastal habitat, 

 there is no evidence that rainfall is a dominant and constant condition 

 determining the annual increment of woody tissue. 



Growth as a Problem in Permeability, by D. T. MacDougal. 



The cell of the plant in its earliest stage is a "solid" unit of colloidal ma- 

 terial which increases by the formation of new particles or ions of substances 

 such as pentosans, albumins, lipins, or soaps within its mass. This accretion 

 stage, as I have termed it, does not account for more than a small fraction 

 of the total volume of the plant or tissue. The greater part of the expansion 

 or measurable growth of the plant is due to the distention or ballooning of the 

 cells. Spaces or cavities are formed within the protoplasm, and these are 

 enlarged by the pressure of the water which is drawn into them by the 

 osmotic action of the sugars and other organic compounds which are con- 



