NO. I GROWTH LAYERS IN TREE BRANCHES — CLOCK ET AL. 2g 



trees of i6 different species. Of this total, i6 branches were measured 

 at weekly intervals for a full year or more. 



The method of sustained periodic measurements (weekly in the 

 main) was applied to the following coniferous species in the Lub- 

 bock area : Ponderosa pine (i tree, 5 branches), loblolly pine (2 trees, 

 4 branches), a short-leafed yellow pine (TTP 22; i tree, i branch), 

 Arizona cypress (2 trees, 4 branches), and red cedar (2 trees, 2 

 branches). At Washington, D. C, periodic measurements were made 

 on the following species of young fruit trees: Apple (i tree, i 

 branch), cherry (3 trees, 9 branches), peach (i tree, 6 branches), and 

 plum (i tree, 3 branches). Thus the total of sustained periodic meas- 

 urements included 35 branches on 14 trees of 9 different species. 

 Within this total, there occurred 17 cases in which annual measure- 

 ments of one to three years preceded or followed a year of periodic 

 (weekly) measurements. 



Because of the nature of observations and the taking of specimens, 

 many cases developed where it was possible to secure accurate meas- 

 urements of tip growth for intervals varying from approximately a 

 week to a full growing season. These short-interval measurements 

 were made on the following species in the Lubbock area : Conifers — 

 ponderosa pine (6 trees, 26 branches), loblolly pine (2 trees, 12 

 branches), Jeffrey pine (2 trees, 4 branches), a short-leafed yellow 

 pine (MP i; i tree, i branch), another short-leafed yellow pine 

 (TTP 22 ; I tree, 2 branches), Arizona cypress (8 trees, 55 branches), 

 and red cedar (3 trees, 14 branches). Dicotyledons — apple (3 trees, 

 14 branches), ash (i tree, i branch), Siberian elm (i tree, 2 

 branches), cotton wood (i tree, 3 branches), honey locust (4 trees, 

 8 branches), silver maple (2 trees, 10 branches), sycamore (i tree, 

 I branch), and vitex (i tree, i branch). In the mountains of northern 

 New Mexico, the following species were measured for short-interval tip 

 growth : Conifers — foxtail pine ( i tree, i branch) , corkbark fir ( i tree, 

 I branch), and Engelmann spruce (i tree, i branch). Dicotyledons — 

 gooseberry (i shrub, i branch). At Washington, D. C, the following 

 species were measured in the same manner: Apple (i tree, i branch), 

 cherry (3 trees, 9 branches), peach (i tree, 15 branches), and plum 

 (i tree, 2 branches). The total of all short-interval measurements, 

 therefore, included 185 branches from 47 trees of 23 different species. 

 Of this total, there were 137 cases of short-interval measurements on 

 branches which were in turn measured annually for an interval of 

 one to four years. 



In addition to actual measurements made either annually or peri- 

 odically, a third method of obtaining tip-growth increments em- 



