GROWTH IN TREES. 29 



5 mm., of which nearly one-half was lost in the last week of August. 

 Another slight swelling began September 14, terminating October 5, 

 after which equalizing daily variations occurred until the instrument 

 was dismounted October 22 1 (fig. 9). 



The total enlargements amounted to about 10 mm. and the total 

 shrinkage during the season to about 5 mm. It is obvious that the 

 woody layers formed in such an interrupted cycle of growth must be 

 difficult of interpretation by the observers who seek to obtain the 

 history of the tree from its "annual rings." Dr. Shreve has found 

 that individuals of this species form two such rings in locations at 

 slightly greater altitude but similar climatic conditions. 2 



A dendrograph was attached to a yellow-pine tree (Pinus scopulorum) 

 at the Fort Valley Forest Experiment Station near Flagstaff, Arizona, 

 late in April 1920. This tree was about 45 cm. in diameter and had 

 apparently ceased growth or was quiescent during this season. No 

 permanent change in diameter amounting to as much as a millimeter 

 occurred during the summer. Equalizing variations were marked, 

 however, during the latter half of July, after which the record showed 

 but little variation. Mr. G. A. Pearson, in charge of the Experiment 

 Station, reports that this tree showed some growth of branches and 

 terminals in 192 1. 3 



A dendrograph was installed on the basal section of a yellow pine 

 (Pinus ponderosa) at the Alpine Laboratory, which made a record 

 from June 5 to September 15, 1920. Mr. Loftfield, who was in charge 

 of the instrument, reports that this tree was nearly 36 cm. in diameter 

 and that it stood on an east-southeast slope near the Douglas fir which 

 was also measured. Thermographic and hygrographic records were 

 obtained which pertain to both trees. As the instrument was set to 

 amplify 15 times, the daily equalizing variations appeared very marked 

 at the beginning, amounting to as much as 0.5 mm. in diameter daily. 

 An increase in diameter was noticeable on June 14, on which date an 

 inch of rainfall was noted, but this was only a temporary increase, as 

 equalization followed. A week later the buds awoke and disturbances 

 of the daily variation ensued. The branches reached full length early 

 in July and the leaves full size by the middle of the month, but not 

 until a month later (August 12), in a period of heavy rains, did an 

 increase take place. This continued until September 4, and during 

 this period of 23 days a net enlargement of nearly 2 mm. in diameter had 

 taken place, after which some shrinkage accompanied the daily 



1 The above statements are to be taken in correction of the preliminary notice on the growth of 

 the Chihuahua pine in Carnegie Inst. Wash. Year Book for 1918, p. 75. 



2 Shreve, F. The density of stand and rate of growth of Arizona yellow pine as influenced by 

 climatic conditions. Jour. Forestry, 15:695-707. Oct. 1917. 



3 Pearson, G. A. The relation between spring precipitation and height-growth of western 

 yellow pine saplings in Arizona. Jour. Forestry, 16: 677-689. 1918. Boerker, R. H. Rela- 

 tion between height-growth of larch seedlings and weather conditions. Jour. Forestry, 16:861 

 870. Dec. 1918. 



