iQisl 



BROWN— 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. Sanio 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 



2 year twig . . . 



6 year twig . . . 

 12 ft. from apex 

 25 ft. from apex 

 38 ft. from apex 

 51 ft. from apex 



Thickness of catabium 



Cell rows in cambium 



Average width of 

 last formed rings 



5- 



S- 9 

 29-31 

 32-40 

 29-35 

 29-35 



9^ 



2- 4 

 2- 4 



6- 7 



7- 9 

 7-10 



7- 9 



691. CM 

 661.0 



3367.0 

 4297.6 

 3013 -8 

 2894 . o 



