OF TREE BRANCHES AT FREEZING TEMPERATURES 55 
observations described have made an advance in the study of the 
subject. Some of the facts which have been determined are 
summarized below; temperatures are given in Fahrenheit for 
reasons previously stated. 
1. The measurements which have been made on the move- 
ments of large branches of the European linden (Tilia europaea), 
due to a reduction of the atmospheric temperature seem to show 
that below 32° F. the movements are thermometric; when the 
temperature of the air falls below the freezing point of water 
(32° F.) (or very shortly above that point) the depression of the 
branches begins, and continues until at least o° F., the lowest 
point at which observations were made. 
2. There is scarcely any movement above 32° F., the level of a 
branch at 70° F. being approximately the same as at pe Me 
The freezing action of water (the aqueous part of a solution) 
is therefore the origin of the process which brings about the 
change in shape of the branch with change of temperature below 
32° F. There seems, however, to be a.very slight thermometric 
movement just above 32° F., the data on which is uncertain. 
3. By making hourly observations not made hitherto, it has 
been shown that there may be a lag of one or two hours in the 
movements of the branches behind the changes of temperature, 
but if the air temperature is changing, a very slight change in 
the rate causes an almost immediate modification in the rate of 
movement of the branch. The observations made thus far indi- 
cate that a constant state of temperature for a considerable time, 
slightly below 32° F., causes a small movement; then the branch 
remains stationary until the temperature changes. These facts 
lead to the conclusion that the freezing liquid bringing about 
the thermometric movements of the branches below freezing tem- 
peratures is not pure water, but a solution, namely, the sap. 
4. By artificially depressing the branches by means of weights, 
it was found that strains in the wood cause the branch to become 
temporarily depressed by a small amount. These strains in the 
branch, and the effect of lag of position of the branch behind the 
temperature of the air, explain the fact that in the curves showing 
the relation of the position of a branch to air temperatures the 
points are somewhat inconsistent. 
