CORRELATION AND GROWTH IN THE BRANCHES 
OF YOUNG PEAR TREES 1 
By H: S. Reed 2 
Professor of Plant Physiology, College of Agriculture, University of California 
The present paper attempts to make a quantitative study of the rela¬ 
tionships of laterals produced by the young branches of the pear tree. 
Such an inquiry should be of value both to the physiologist who is in¬ 
terested in the mechanism of development and to the horticulturist who 
is interested in the production of a tree of a given type. 
In a previous paper (ro) 3 it was shown that upright young pear shoots 
tend to remain unbranched so long as the apical bud grows uninter¬ 
ruptedly. If the apical bud is arrested in its development, or is removed, 
a neighboring lateral bud promptly develops and continues the lineal 
growth of that member. Moreover, if the apical portion of a shoot is 
amputated, the buds immediately below the point of amputation are not 
only the first to develop into shoots but produce the longest shoots. 
A plantation of young Bartlett pear trees (Pyrus communis L.) growing 
at the Citrus Experiment Station, Riverside, Calif., furnished the data 
upon which this study is based. The trees were planted in the orchard 
in 1916, and the measurements were taken in February, 1920. The 
lateral shoots (PI. 142), hereafter designated as “laterals,” grew during 
the summer of 1919, and the mother shoots on which they were borne 
grew in the summer of 1918. 
During the early life of the orchard, certain plots of the trees were 
systematically “headed back” to form a framework of a particular type. 
Accordingly these plots of trees were pruned in the winter of 19x8-19 by 
amputating from one-half to three-fourths of all of the principal upright 
shoots grown in the preceding season. The portion remaining after 
pruning is designated as the “mother shoot” in the following discussion. 
The unpruned trees never received any pruning after the first year. The 
lateral shoots grew on the mother shoots during the summer of 1919. 
The relations of the two will be readily comprehended upon referring to 
Plate 142. 
The mother shoots used in this study stood in an approximately 
vertical position and on the small trees were in no way crowded. The 
results are not, therefore, believed to be greatly influenced by differences 
1 Paper No. 78, University of California, Graduate School of Tropical Agriculture and Citrus Experiment 
Station, Riverside, Calif. 
2 The writer wishes to mention his indebtedness to Mr. F. F. Halma for assistance in the calculations and 
to Dr. J. A. Harris for valuable suggestions. 
3 Reference is made by number (italic) to “literature cited,” p. 874-875. 
(849) 
Journal of Agricultural Research, 
Washington, D. C. 
zk 
Vol.XXI, No. ri 
Sept. 1, 1921 
Key No. Calif.-31 
