KNUDSON: CAMBIUM DEVELOPMENT IN AMERICAN LARCH 283 



TABLE VII 



TOTAL NUMBER OF NEW ROWS AND DIAMETER OF PHLOEM, CAMBIUM AND XYLEM CELLS 



IN TREES B AND D 



The season of diameter growth in larch is relatively short. 

 Practically all of the growth occurred during the month of June. 

 The small increase produced from the time of bud opening, April 

 19 to May 25, consisted entirely of cambium and phloem develop- 

 ment. The diameter increases of trees A and C and B and D 

 during the season 1909 are graphically represented in DIAGRAM IK 



INVESTIGATION OF 1911 



Since the studies made in 1909 indicated that growth in 

 diameter first occurred in the middle region of the trunk and not 

 at the base or apex, it seemed advisable to continue these studies 

 with respect to the development in the lateral branches. The 

 investigation was made with the object of answering the three 

 following questions: (i) Does inception of diameter increase begin 

 first in the topmost branches, in the middle, or in the basal, 

 branches? (2) In what part of the individual branches does 

 diameter increase begin? (3) Does xylem development in the 

 lateral branches precede that in the trunk? 



For this investigation a larch tree of approximately 10 years 

 of age was used. It was growing isolated, about 100 feet from 

 the trees mentioned above, growing in the nursery row. For con- 

 venience this tree is hereafter designated as tree E. On May 22, 

 from each of the whorls of branches from apex to base, one branch 



