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 fiow of sap often 

 begins when the ground is covered with one or two feet 

 of snow, and when we cannot suppose tlie 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 sufiiciently 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 Tharaud, Saxony, under direction of Stoeclihardt, 

 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 mininmm of water in the wood occurred in May, June, and 

 July ; in the bark, much irregularity was observed. Cliem. Ack^rsmann, 1806, 

 p. 159. 



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