GROWTH STUDIES IN FOREST TREES 



I. PINUS RIGID A MILL' 



Harry P. Brown 



(with plates XXIV AND XXV) 



The phenomenon of tree growth has long been a subject of 

 investigation. Sachs, Hugo de Vries, Noedlinger, Mer, the 

 Hartigs, Wieler, BtJSGEN, VON MoHL, and a host of others have 

 worked on problems concerned with it, and many papers presenting 

 the results of investigations are to be found in the literature of the 

 last half-century. 



As might be expected, the question has resolved itself into a 

 number of minor topics, each with its coterie of followers. Some 

 have placed particular stress on spring and summer wood forma- 

 tion; others have studied growth as related to external factors or 

 to inheritance. Various instruments have been devised to measure 

 tree growth, and one author (Reuss 12) goes so far as to assert 

 that thunderstorms cause a growth stimulus in trees. Investiga- 

 tions deahng with every phase of the subject are described in 

 exhaustive detail, and yet with rare exception there is a maze of 

 conflicting opinion sufficient to confuse even the careful reader. 



The present studies were undertaken with a twofold purpose, 

 namely, to clear up disputed joints regarding annual ring forma- 

 tion in trees and to formulate laws of tree growth. Investigations 

 were carried on upon various forest trees with this idea in view. 

 The results of those on Pinus rigida are embodied in this paper. 



Secondary thickening in trees arises as a general rule from a 

 cambium which lives from year to year. This annually passes 

 through certain active and certain dormant periods. The latter 

 assertion, however, is to be taken in its broadest sense. In many 

 tropical woods the interruption to growth can be detected only with 

 a microscope, while in others it is totally lacking; the wood appears 



' Contribution from the Department of Botany, Cornell University. No. 148. 

 Botanical Gazette, vol. 54] [386 



