OF SAP IN PLANTS. 41 



Salix alba, — A young leafy shoot 12 inches long was stripped 

 of its bark for 2 inches at the bottom, and dipped 1 inch in the 

 jfluid ; 1 inch below the top (the upper oblique cross section of 

 the shoot) an annular piece of bark 3 lines wide was removed. 

 Protected from drying as before. After six days the salt was 

 found to have ascended into the very apex, and indeed into all 

 parts, but most strongly in the medullary sheath. This con- 

 tained dark blue dotted vessels and unrollable spirals. Only the 

 epidermis of the upper piece of bark gave no reaction. 



S. alba. — A piece 12 inches long was cut out of a young leafy 

 shoot, 2 inches of bark removed at the bottom, and dipped 



1 inch into the solution. In the upper part a little ring of bark 

 was cut out, and the whole allowed to stand without protection 

 from evaporation. After six days, all parts, up to the top of the 

 shoot, even the externally dry, exposed part of the wood which 

 had been laid bare, gave a reaction. At the extreme point the 

 vessels of the medullary sheath no longer took part, but the 

 inner prosenchymatous cells of the wood reacted deep blue. 



From these experiments it is seen how little share the bark 

 takes in the conduction of the sap, and how readily a horizontal 

 movement of the sap takes place from the gorged young wood 

 into the bark. 



S, alba. — Absorption through the barh — A piece 12 inches 

 long, of a young leafy shoot, was taken and the bark slit up 



2 inches from the bottom drawn back, and the exposed cylinder 

 of wood, 2 inches long, removed ; then the lower end (merely 

 bark) was dipped 1 inch into the solution. After six days the 

 shoot was found remarkably dry, from insufficient supply of 

 fluid. — Analysis. The whole of the stripped piece of bark, even 

 the epidermis, reacted strongly. The wood had likewise ab- 

 sorbed fluid from the bark into all parts at the lower end, but 

 not uniformly ; particular vessels and cells did not react at all. 

 — Cross section 2 inches higher up. The bark and medullary 

 sheath had absorbed most, the pith least. At 3 inches distance 

 from the lower end of the wood, the salt was found only in liber 

 and wood ; the epidermis and pith no longer reacted. 



Consequently, under favourable circumstances, a movement of 

 the fluids in the bark, and horizontally from the bark into the 

 wood, undoubtedly occurs, although to a very slight extent. 



