191 5] BROW N—PINUS STROBUS 203 
The resting cambium as seen in cross-section consists of 2-10 
layers of tabular cells lying just outside the last formed xylem 
elements. Santo and other early anatomists considered the cam- 
bium as consisting of a single initial layer, which through repeated 
division gave off daughter cells centripetally and centrifugally. 
These divided a second time, and the resulting cells enlarged and 
became elements of the phloem or xylem. The initial layer, if 
present in white pine, cannot be distinguished as such. The cells 
in each layer of the merismatic tissue are similar to the others in 
size, form, and protoplasmic content. The number of layers of 
cells in the cambium apparently varies between rather wide limits. 
Such variability might lead one to think that the work was not 
accurately done. The figures given above are as exact as the 
material permitted. The cambium is a very variable tissue both 
in number of cell layers and thickness of the same. Data indicating 
this (table A) were computed from measurements on tree I, a 
description of which follows. 
Tree I was a thrifty specimen of white pine standing near the 
edge of a mixed stand on the brow of an incline which sloped north- 
ward into Six Mile Creek valley. The height of the tree was 55 
feet, and crown development extended to within 18 feet of the 
ground. The tree was directly exposed to the south. Ground 
cover included sparse brush and pronounced sod formation. Cut- 
tings were first made on this tree in August 1912, at heights of 4, 
17, 30, and 43 feet from the ground, and were repeated at frequent 
intervals until September 1913, as recorded in the tables. Twig 
cuttings from near the top of the crown were also taken from time 
to time. The data in the table are from the cuttings of February 
20, 1913. 
TABLE A 
WINTER CONDITION OF CAMBIUM, TREE I 
Cutting Thick f bi Cell rows in cambium Faby adel ge tog 
o year twee... ok. 5- on 2-4 691.04 
OV WE 5-9 2- 4 661.0 
12 ft. from apex... .. 29-31 6-7 3367.0 
25 ft. from apex..... 32-40 - 4297.6 
38 ft. from apex... .. 29-35 7-10 3013.8 
51 ft. from apex. .... 20-35 — 2894.0 
