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 



