KNUDSON: CAMBIUM DEVELOPMENT IN AMERICAN LARCH 287 



in the middle branches. This increase corresponds with the re- 

 sults secured previously on the diameter increase in the trunk, 

 in which it was found that the growth first began in the middle 

 region. 



In regard to the second question as to the region of the branch 

 in which growth first occurs, TABLE x is suggestive. The figures 

 of the following table are the averages of the seven apical cuttings, 

 the seven basal cuttings and the average diameter of xylem in the 

 middle regions of the seven branches. 



TABLE X 



AVERAGE DIAMETER INCREASE OF XYLEM AT APEX, MIDDLE, AND BASE OF ALL LATERAL 



BRANCHES 



Region of Diameter increase 



cutting of xylem 



Apical 20.8 fj. 



Middle 7-5M 



Basal 2.5/x 



From previous results it was expected that the growth would 

 first occur in the middle of the branch, but the evidence indicates 

 that the development of xylem in the lateral branches begins at 

 the apex and then continues towards the base. The opening of 

 the buds, however, does not follow the same order. On April 26, 

 1911, the lateral branches of a tree in the nursery row were ex- 

 amined and it was found that buds on the one and two years old 

 wood had not yet opened, on the third year wood the leaves were 

 just protruding while on the older wood the buds were fully opened. 



In regard to the third question, " Does diameter increase in 

 the twigs and branches precede that in the trunk?" the following 

 observations were made. From the same tree from which the 

 cuttings from the lateral branches were removed and on the same 

 day, namely, May 22, cuttings were removed from the apex to 

 the base of the trunk. Seven such cuttings were removed from 

 the south side of the tree, one cutting just below each whorl of 

 branches. From a study of slides prepared from the material the 

 following figures have been obtained. (See TABLE xi.) There 

 are also included in TABLE xi figures derived from cuttings made 

 on June 6. 



A comparison of the figures for May 22 with the figures for 

 growth in the lateral branches (see DIAGRAM in) reveals the fact 



