204 BOTANICAL GAZETTE : [MARCH 
It follows from the table that in white pine trees which are 
growing rapidly, the cambium is smallest both in number of cells 
and thickness in the smaller twigs and branches. It increases 
gradually in thickness and number of cell layers until that point 
is reached in the bole where diameter growth is a maximum. The 
decrease in the figures indicating the dimensions of the cambium 
are not proportional thereafter with the decrease in growth in 
diameter. It would appear as if the cambial layer, once it had 
attained its largest proportions, varied little in vigorous trees. 
In suppressed trees, however, it may reasonably be assumed that 
the cambial layers fall off in number and thickness toward the base 
of the shaft, but in such cases the reduction is not closely correlated 
with decrease in the width of the completed annual ring. 
Another point relating to the cambial and phloem tissues 
deserves description here. I refer to the statement commonly 
made in textbooks that while the formation of xylem ceases early, 
the cambium continues to form phloem as long as climatic condi- 
tions are favorable. It is of interest to note in this connection the 
condition of the young phloem and cambium on September 26, 
1912, and February 22, 1913. In all four cuttings of the first 
named date we find the condition as shown in fig. 7. Xylem forma- 
tion had apparently ceased, the cell walls in the last row of tracheids 
were still in the process of thickening, but no new elements were 
being added. In the phloem we find a broad band of sieve tubes 
with a few parenchyma cells interspersed among them, making up 
in all some 15 rows of cells. This represents, with the possible 
addition of two or three rows of partly crushed elements to the 
outside, the seasonal growth of phloem. It is to be noted here 
that none or very little compression had occurred. 
Comparing the above with what occurred on February 20, 1913 
(figs. 2 and 3), the following interesting changes are to be found. 
Contraction had taken place, due to low temperatures during the 
winter, but not all of the sieve tubes are flattened to the same 
extent. In each of the four cuttings of February 22, the 3-5 last 
formed sieve tubes are only partially distorted by pressure, and 
those in the higher cutting (fig. 2) noticeably more so than in the 
lower cutting (fig. 3). In the last case there is a sharp dividing 
