548 THE NATURE OF THE GROWTH RATE 



The data suggest that each shoot has a more or less independent 

 supply of the catalytic agent which exercises such an important in- 

 fluence upon the rate at which growth proceeds. 



The Growth Rate of Young Walnut Trees. 



The data upon which this study is based were obtained from mate- 

 rial growing in the grounds of the Citrus Experiment Station at 

 Riverside. 



In the spring of 1916 seeds of Juglans nigra L. (black walnut) had 

 been planted in rows for nursery propagation work. The young trees 

 which grew from these seeds were used for study in the summer of 

 1917; i.e., during their second season of growth. A part of the trees 

 were grafted in the spring of 1917 with scions of Juglans regia (Per- 

 sian walnut). A few weeks after growth from the scions started, all 

 new shoots were removed, except one which furnished the data for 

 the observations on this species. The balance of the Juglans nigra 

 trees grew on during the second summer. 



The Juglans nigra seedlings were selected on April 17 and marked 

 by a line of India ink on the stem from which the distance to the 

 terminal bud could be measured when desired. From a portion of 

 the trees all laterals on the wood of the previous year were removed 

 before measurements were begun, and the observations on these pruned 

 trees were separately recorded. The growth from the Juglans regia 

 scions was soon sufficient to afford measurements, and they were 

 marked on May 29. 



Measurements were made at each day of observation to determine 

 the height of the tree stem from the ink mark to the terminal bud of 

 the main axis. This could be ascertained with comparatively little 

 error. It was pla'nned to make measurements at intervals of 7 days, 

 but other circumstances made it necessary to vary this interval at 

 times. The exact length of the intervals is stated in Table II. 



The population thus gave an opportunity for studying the follow- 

 ing points : {a) the growth of seedling trees in the 2nd year of their 

 life; (&) the growth of similar trees from which all laterals had been 

 removed at the beginning of the 2nd year; and (cj the growth from 

 scions of a distinct species growing on the same roots as (a) and {b). 



