NO. I GROWTH LAYERS IN TREE BRANCHES — CLOCK ET AL. 3 



to a large number of additional individuals who in one way or another 

 contributed materially to the progress of our work. 



Especially to Dr. I. W. Bailey do we owe a large measure of grati- 

 tude for demonstrating the anatomy of natural frost injury. The 

 recognition of such injury along with its recovery actually formed the 

 starting point of the present work. 



Appreciation is expressed to Texas Technological College for the 

 use of many facilities needed during the long period of time required 

 for the completion of the work. Also appreciation is due Macalester 

 College for use of similar facilities since 1948. 



We are indebted to D. C. Dornberg of Saint Paul for many hours 

 of careful work with the bulk of the photographs here included and 

 to J. B. McBurney who prepared figures 34 and 35 and who gener- 

 ously assisted with the interpretative diagrams. 



No detailed review of literature has been included in this report 

 because several extensive reviews covering this subject have been pub- 

 lished in the Botanical Review (Clock, 1941, 1955a; Studhalter, 

 1955). 



11. THE TREES USED 



LOCATION AND ENVIRONMENT 



The plants used included both native and cultivated trees and 

 shrubs. The great majority came from native species of trees planted 

 on the campus of Texas Technological College or its immediate vicin- 

 ity at Lubbock, Tex., where ecologic conditions are typical of the ex- 

 treme lower forest border. However, comparisons were made with a 

 natural forest-border area, with a systematically irrigated area, with 

 an east-coast area, and with forest interiors. Natural forests occur 

 below the Break of the Plains 35 to 55 miles east of Lubbock, in the 

 mountains of New Mexico 260 miles northwestward, and in the 

 Chisos Mountains 320 miles southward. 



It is important to note that comparative studies revealed a close 

 similarity between the growth-layer patterns of the planted trees at 

 Lubbock and the patterns of the trees in the natural forests east of 

 Lubbock. 



LUBBOCK, TEXAS, AND VICINITY 



This area supplied most of the trees for experimental purposes. 

 The city of Lubbock lies in northwest Texas on the southern part of 

 the High Plains at an elevation of 3,200 feet. On the whole, the 



