The thermometric movements of tree branches at freezing 
temperatures* 
C. C. TROWBRIDGE 
(WITH NINETEEN TEXT FIGURES) 
During the winter of 1910, the writer of the present paper 
noticed that the branches of several linden trees on the grounds 
of Columbia University in the City of New York changed their | 
position when a fall of temperature below freezing occurred. 
Fic. 1. Photograph showing the extent of the change of the position ot a 
branch of a European linden tree (Tilia europaea) between normal and about twenty- 
two degrees below freezing, Fahrenheit. The lower branch (M) has been artificially 
inserted in the photograph to show extent of movement. Lower branch, at elbow, 
M, 5.33 ft. elevation, temp. + 10° F., February 10,1912. Upper branch, at elbow, 
N, i 82 ft. elevation, i + 35.6° F., February 28, 1912. This branch is desig- 
s ‘Branch A e No. 1,” in the accompanying curves. 
. es ee of the Phoenix Physical Laboratory, No. 34. 
29 
