288 KNUDSON: CAMBIUM DEVELOPMENT IN AMERICAN LARCH 



TABLE XI 

 NUMBER OF ROWS OF XYLEM CELLS AND DIAMETER INCREASE OF XYLEM IN TREE E 



that except for the apical part of the trunk the growth there has 

 been much greater than in the branches. The average diameter 

 increase of xylem in all the branches was by May 22 only 10.7 /z, 

 and the average number of cells in the new xylem layer only 0.62. 

 The greatest diameter increase in the branches was only 37 ju, 

 while the average for the trunk was 5.8 cells with a diameter of 

 139 ju. If reference is made to TABLE vin it will be seen that no 

 growth occurred in branch No. 2 while in the trunk at this region 

 the increase was 55.5 u. The average diameter of xylem in 

 branch No. 7 was only 4-5 /*, while in the region of the trunk from 

 which the branch was secured the diameter increase amounted to 

 229 /*. It is very evident, therefore, that in a larch of this age 

 under isolated conditions growth does not begin first in the twigs 

 and then extend to the trunk, but rather it begins first in the 

 trunk. 



The figures in TABLE xi give no strong indication of the region 

 in which growth first began. The diameter increase was greatest 

 just below the 4th, 6th, and 7th whorls of branches. No increase 

 was manifest near the apex. 



Region of cutting 

 in trunk 



TABLE XII 



No. of rows of xylem 

 cells 



Below ist whorl Cutting lost 



Below 5th whorl 4 



Below 7th whorl 9 



Below 9th whorl 5 



Dia. increase 

 of xylem 



III At 

 222 fJi 

 129 At 



In order further to check the work of 1909 a few cuttings were 

 made from another tree in the nursery row on May 22. This tree 



