DEPARTMENT OF BOTANICAL RESEARCH. 75 



The care of this instrument and of the records of temperature were 

 shared by Dr. H. W. Fenner in May and June, and the entire experi- 

 ment was in the hands of Mr. B. R. Bovee during June, July, and 

 August. Mr. Bovee also made weekly trips to the instrument attached 

 to the Chihuahua pine, 22 miles distant, with a chmb of 4,000 feet. 



Growth of the Chihuahua Pine, by D. T. MacDougal. 



A dendrograph with a yoke of bario was carried by pack animals up 

 a trail in the Santa Catalina Mountains in Arizona and attached to a 

 tree of Pinus chihuahuana, 40 cm. in diameter, on April 4, 1918. This 

 tree stood at an elevation of about 6,000 feet, at the extreme lower 

 margin of its habitat. Some enlargement was exhibited from April 14 to 

 May 4. After a period of quiescence and shrinkage, enlargement again 

 began on May 28 and continued to June 14. A second period of quies- 

 cence intervened, with marked shrinkage during late June, which con- 

 tinued well into the summer rainy season, enlargement not being 

 resumed until Julj'^ 20. This continued until mid-October. 



The increase of the trunk and included bark during the first period 

 was about 2 mm., of which 1 mm. was lost in the ensuing quiescent 

 period. A gain of 2 mm. was made in the second period, with a shrink- 

 age of 3 mm. during the hot midsummer period preceding the summer 

 rains. While presumptively some wood may have been formed, the 

 diameter on July 20 was no greater than on April 4. An increase of 3 

 mm. had taken place by August 16 and was still in progress on that 

 date. The daily variation was of the type which is described for the 

 Monterey pine in the following paragraph. The shrinkage was great- 

 est late in June, before the midday formation of cumulus clouds 

 began, and the cambial region at this time took on temperatures of 

 25° and 27° C. 



The fact that enlargement did not begin until after 3 weeks of the 

 summer rainfall had passed is of no small interest. The temperatures 

 of the cambial region at this time were about 18° and 20° C. Young 

 cones had been formed and the pollen crop shed before measurements 

 were begun, and some elongation of the branches had taken place. 

 It is to be noted that the trunks of this tree show a double annual 

 ring, a fact discovered and described by Dr. Shreve. (The density 

 of stand and rate of growth of Arizona yellow pine as influenced 

 by climatic conditions. Jour. Forestry, vol. 15, 695-707. Oct. 1917.) 



The Growth of the Monterey Pine, by D. T. MacDougal. 



The Monterey pine (Pinus radiata), which is native in a restricted 

 region within a short radius of the Coastal Laboratory, is noted for 

 its rapid growth and short life period. The conditions about Carmel 

 are such that the species shows growth practically throughout the year, 



