198 BAILEY AND TUPPER. 



mother cells which form them and (2) the amount of elongation which 

 they undergo during differentiation. A detailed discussion of the size 

 variations of cambial cells, and the elongation of their daughter cells 

 during differentiation, will be undertaken in the second paper of this 

 series. 



Acknowledgments. 



The writers are greatly indebted to Professors R. T. Baker, H. 

 Shirasana, C. J. Chamberlain, O. W. Caldwell, W. P. Thompson, and 

 R. T. Fisher; Messrs. R. D. Swales of the Union Lumber Company, 

 Ralph Staebner of the Little River Lumber Company, R. R. Chaffee 

 of Endeavor, Pa., and H. N. Lee of the Canadian Forest Products 

 Laboratory; and the following members of the U. S. Forest Service 

 (Wm. N. Cluigan, Knower Mills, George Donaldson, Austin Cary, 

 Eloise Gerry, Arthur Koehler, W. D. Brush, R. T. Ferguson, J. B. 

 Connor and Ward Shepard) for their kindness in sending material of 

 various plants, and to Raphael Zou and Bertha Kaplan for assistance 

 with the Russian literature. 



BussET Institution, ' 



Jamaica Plain, Mass. 



