; : ; ve, ‘ 
Observations on the inception, season, and duration of cambium 
development in the American larch {Larix laricina 
(Du Roi) Koch,] * 
L. KNupson 
(WITH PLATES 18 AND 19) 
INTRODUCTORY 
During the past twenty-five years very little attention has been 
devoted to a minute study of the diameter increase in trees. 
Comparatively little is known concerning the season of wood 
formation; and with respect to the region of the tree in which 
diameter increase first begins, the evidence is contradictory. 
With the object of determining the part of the tree in which 
cambial activity begins, as well as to determine the season of 
growth, investigations were begun during the season of 1909 and 
continued in 1911. The results obtained from the study of mate- 
rial collected these two seasons form the basis of this paper. 
The subject was suggested by Prof. W. W. Rowlee, and to 
him, as well as to Prof. B. M. Duggar, the writer is indebted for 
helpful suggestions. 
HISTORICAL 
The work of von Nordlinger, Th. Hartig, Robt. Hartig, Mer, 
and others has thrown some light upon the extent and duration of 
cambial activity. They have found, in general, that under 
forest conditions growth first begins in the youngest twigs and 
then proceeds downward into the older regions. Less work has 
been done on the cambial activity in isolated trees. 
Concerning the region of first cambial activity, Th. Hartigt 
concluded that it occurred in the youngest twigs and then gradu- 
ally extended downward. In a 30-year old Pinus sylvestris, and 
also in oak, cambial activity began almost simultaneously over 
the entire trunk, while in larch and maple of the same age cambial 
* Laboratory of Plant Physiology, Cornell University, Contribution No. 8. 
+ Hartig, T. Anatomie und Physiologie der Holzpflanzen, 368. 1878. 
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