300 
and it was found that, as a rule, the expan- 
sions and contractions were in the same direc- 
tion as for the transverse measurements, but 
yet this was not always the case. The 
changes in circumference were found not to 
be proportional to the transverse measure- 
ments. After more than four months, when 
the temperature was much higher than at the 
time observations were begun, the cireumfer- 
ence of the tree was still smaller than when the 
first observations were made. The method of 
making observations on the circumference con- 
sisted in measuring, with a pair of dividers, 
the distance between two scratches on a 
painted steel tape surrounding the tree, and 
continuously left in contact with it. When 
the series of observations was begun, two 
scratches were made, one on each of the two 
parts of the tape which lay, one directly above 
the other, and, as the circumference changed, 
the distance between these scratches was re- 
corded. These measurements were made sev- 
eral times a day, and showed that the final con- 
traction, which Grossenbacher? thought might 
possibly be due to an error in his measure- 
ments, is an actual experimental fact. Gros- 
senbacher’s observations were made at inter- 
vals of several weeks, and his tape was re- 
moved after each observation. 3 
An equally extended series of measurements 
on frost cracks was made during the winter of 
1917-18. It was found that during the coldest 
weather when the crack was open about three 
fourths of an inch, its depth at certain points 
was more than ten inches. Also, in addition to 
the large crack formed on the south side of the 
linden tree, another was formed on the north 
side toward the end of January, 1918, and the 
change in the width of the two cracks seemed 
to follow the same law, 2. e., the cracks became 
wider as the temperature fell, and narrower as 
it rose again. 
From the measurements on the transverse 
changes, on the circumference and on frost 
eracks, the conclusion was reached that frost 
2J. G. Grossenbacher, ‘‘Crown-Rot of Fruit 
Trees, Field Studies,’’? N. Y. Agricultural Experi- 
ment Station, Geneva, N. Y., Technical Bulletin, 
No. 23, September, 1912, pp. 35-37. 
SCIENCE 
[N. 8. Vou. XLVIITI. No. 1240 
eracks are caused by a tearing apart of the 
tissue of the tree, due to a great contraction. 
Both the circumference and the transverse di- 
Mensions are much less when the crack is open 
than when it is closed, and the one is not pro- 
portional to the other. Frost cracks are prob- 
ably due to a difference in the coefiicients of 
radial and tangential contraction of the tree, ° 
a difference which sets in at approximately 25° 
Fahrenheit (about 4 degrees below zero Centi- 
grade). If the cells of the tree collapse in a 
tangential direction (a fact which was ob- 
served) and the changes along the medullary 
rays are not as great, then the tree will split 
open, due to the increased tension. If the 
cells again expand tangentially, the crack will 
close due to increased pressure, provided the 
radius may not change in dimensions at all, 
it may expand to a greater extent, or it may 
even contract; in any case the crack will close. 
The first or third of these cases would account 
for the observation that after the crack has 
closed, the circumference of the tree is less 
than before it opened. These conclusions are, 
however, tentative and approximate, due to the 
complications caused by the lag in the tan- 
gential direction, the temperature gradient 
through the tree, and other difficulties which 
must still be studied, before a more complete 
explanation can be given. 
C. C. TRowBrinGe,* 
Mase, WEIL 
PH@NIX PHYSICAL LABORATORIES, 
CoLuMBIA UNIVERSITY 
THE DEPTH OF DOLOMITIZATION? 
Ty a recent issue of the American Journal of 
Science,2 there appeared an article by E. W. 
Skeats on “The Formation of Dolomite and 
its Bearing on the Coral Reef Problem.” The 
author of this paper adopts the replacement 
theory of the origin of dolomite and presents 
3 Some similar conclusions were reached by a dif- 
ferent method by Caspany, Bot. Zeit., 15, 1857. 
4 Deceased. 
1 Published with the permission of the Director 
of the Iowa Geological Survey. 
2Volume XLV., 4th Series, pp. 185-200, March, 
1918. 
