MOTION OF THE JUICES. 333 
water, and never more so than in winter.* This water is 
either pumped into the plant, so to speak, by the root- 
power already noticed (p. 248,) or it is generated in the 
trunk itself The water contained in the stem in cold 
weather is undoubtedly that raised from the soil in the 
autumn. That which first flows from an augur-hole, in 
March, may be simply what was thus stored in the trunk; 
but, as the escape of sap goes on for 14 to.20 days at the 
rate of several gallons per day from a single tree, new 
quantities of water must be continually supplied. That 
these are pumped in from the root is, at first thought, dif- 
ficult to understand, because as we have seen (p. 250) the 
root-power is suspended by a certain low temperature 
(unknown in case of the maple) and the flow of sap often 
begins when the ground is covered with one or two feet 
of snow, and when we cannot suppose the soil to have a 
higher temperature than it had during the previous win- 
ter months. Nevertheless, it must be that the deeper 
roots are warm enough to be active all the winter through, 
and that they begin their action as soon as the trunk ac- 
quires a temperature sufficiently high to admit the move- 
ment of water in it. That water may be produced in the 
trunk itself to a slight extent is by no means impossible, 
for chemical changes go on there in spring-time with much. 
rapidity, whereby the sugar of the sap is formed. These 
changes have not been sufficiently investigated, however, 
to prove or disprove the generation of water, and we 
must, in any case, assume that it is the root-power which 
chiefly maintains a pressure of liquid in the tree. 
The issue of sap from the maple tree in the sugar-season 
* Experiments made in Tharand, Saxony, under direction of Stoeckhardt, 
show that the proportion of water, both in the bark and wood of trees, varies 
considerably in different seasons of the year, ranging, in case of the beech, from 
35 to 49 per cent of the fresh-felled tree. The greatest proportion of water in 
the wood was found in the months of December and January; in the bark, in 
March to May. The minimum of water in the wood occurred in May, June, and 
July; in the bark, much irregularity was observed. Chem. Ackersmann, 1866, 
p. 159. 
