Growth of Tree Twigs ia) 
THE GROWTH OF TREE TWIGS. 
C. A. LUDWIG. 
METHODS AND RESULTS. 
During the summer of 1921 the writer made a series of measure- 
ments’ of growing tree twigs. This was with the idea of throwing 
what light might be possible on the nature of the plants and on the 
nature of growth, but more specifically of attempting to determine 
definitely if in the absence of irrigation reliable data can be secured 
in humid regions for determining the normal course of the growth rate. 
There were available two thrifty young peach trees, Prunus Per- 
sica (L.) Stokes, and some plants of flowering dogwood, Cornus florida 
L. The first peach tree was on a slight northern slope and was rather 
tardy in starting growth. The other was on a southern slope but was 
shaded considerably by tall forest trees some distance away. It started 
growth sooner than the other, and as the results to be presented show, 
stopped growing sooner. Neither bore any peaches, as the fruit was 
killed by a late spring freeze. Three of the flowering dogwoods were 
along the south edge of a patch of woodland where they were unshaded 
throughout the summer. A fourth was within the forest and was 
shaded as soon as the forest trees had developed their leaves. The dog- 
wood is well known as a shade enduring tree, and there was no indi- 
cation that the small shaded tree used in this study was diseased or 
weakened by reason of the shading. None of the dogwood trees were 
large enough to bloom this season. The measurements were made from 
the base of the shoot to the base of the terminal bud and were taken 
to the nearest one-eighth inch. They were subject to a maximum ex- 
perimental error of about +- 0.125 inch, aside from the “probable” error 
(error of sampling), on the individual measurements. The experimental 
error of the averages is considerably less, but even the greater error 
would produce only a negligible alteration of the growth curve. 
The shoots measured on the two peach trees were divided into two 
classes: (1) shoots which were not so situated as to be over-topped and 
shaded by others; and (2) shoots which were so situated as to be 
shaded. The means for the shoots of class one of the first tree and 
the corresponding growth increments are given in Table 1. The same data 
are shown graphically in Fig. 1. The weekly rainfall summations are also 
shown at the top of the figure. I am indebted for the rainfall records 
to the local co-operative Weather Bureau station. The number of 
twigs measured was eleven for all dates except March 29th, when it 
was seven, the seven shoots then measured being included in the popu- 
lation of eleven used on all succeeding dates. The data for class two 
of the first tree are given in Table 2, Fig. 2. The number of twigs 
was 19 for March 29th, and 22 for all succeeding dates. 
1— am indebted to my wife, Mrs. Nelle McClurg Ludwig, for necessary aid in 
making and recording these measurements. 
