THE CANADIAN HORTICULTURIST. 140 



The leaves heins? the principal organs of assimilation and perspir- 

 ation, it folknvs that when they have fallen off tliere is no lonuev 

 inuc4i lo*5 of Hiiid tc) tiie tree from these canses. But the power of 

 the roots to al.'sorb nioistnre from the earth is not diminished by the 

 loss of the leaves ; they continue to draw Huid from the earth, and to 

 send it up into tlie tree. This action continues, except as nio lih'ed by 

 extreme cold, all winter ; the fluids are drawn from the soil by the 

 roots and sent into tlie tree, and by the time that spiing has come the 

 tree is full of fluids and every vessel distended with sap. During- tlie 

 Avinter we are not able to find sap ])y cutting the tree, because the 

 process of filling w^ith flaid is gradual. 



M. Biot, many years ago, made some very interesting experiments 

 on the flow of sap, and made a contrivance by which the rate of mo- 

 tion could be measured at any season, and showed that there was 

 considerable activity even in winter. He found that the direction in 

 which the sap moved w^as very considerably affected by frost. AVhen 

 the weather was mild the sap was always ascending ; but when it was 

 freezing w'eather tlie sap flowed down. This he attributed to the con- 

 traction of the sap-vessels by the cold, which forced the sap into the 

 larger vessels which were unaffected by the frost under ground. 

 When, however, the frost was sufficiently severe and continued to 

 reach the roots, then the sap was forced back into the trunk ; but when 

 it came on to thaw and the frost left the ground, the sap returned to 

 the roots. Thus we see that, as a rule, the sap is always ascending 

 and that when it descends it is Ijecause it is forced to do so by some 

 temporary cause, and when that cause ceases to act the sap immedi- 

 ately begins to ascend again. 



In connection with the supposed ascent of the sap in spring, and 

 growing out of it, is the popular idea that this ascent of the sap is the 

 cause of the expansion of the buds and leaves. It would be nearer 

 the truth to say tliat the expansion of the buds and leaves was the 

 cause of the motion of the sap. Any of our readers can make the fol- 

 lowing experiment for themselves, and see the true state of the case. 

 If a tree be cut into or tapped in some of the upright branches near 

 the top very early in the spring, and be again tapped just below the 

 branches on the trunk, and again just above the surface of the ground, 

 it will be found that the sap will flow from the wound that is nearest 

 to the top first, from the one just below the branches next, and last of 



