OF SAP IN PLANTS. 4? 



very little in the pith, but elsewhere in all parts (bark and liber 

 included) as far as the cross-section of the wood, but not beyond 

 this even in the bark. The result was similar after absorption 

 for four days. Even after seven days 5 absorption, the solution 

 had not made its way over the bridge of bark ; indeed this did 

 not itself react, although it was in part perfectly fresh and living. 

 In this case, moreover, the whole of the lower outer part of the 

 twig was densely filled with the saline solution ; even the badly 

 conducting pith of the lower portion of wood reacted distinctly ; 

 the medullary sheath and the peripherical portion of the wood 

 reacted most strongly, especially on that side of the wood corre- 

 sponding to the absorbing leaf. From this it is evident that a 

 far stronger penetration of the fluids than that which occurred 

 here, is requisite to overcome the resistance which liber and bark 

 oppose to the descending sap (see Sect. 4 below). 



This observation rendered it necessary to apply the saline 

 solution immediately to those parts to which the business of 

 conveying the sap down is most frequently attributed, in order 

 to bring the question nearer to a decision. 



2. The Descending Sap with direct absorption by the CAMBIUM 



layer. 



Salix acuminata, Sm. In a branch 1^ inch thick, the bark 

 was slit up, separated to a certain extent, and a piece of filtering 

 paper, many folds thick, soaked in the solution, inserted under 

 it, the wound being then loosely bandaged. After one day 

 (June 15) it was found that the salt had neither ascended nor 

 descended beyond the exposed portion of the wood ; it had only 

 penetrated extremely superficially even in the liber which lay 

 directly upon the paper, and not at all into the rest of the bark 

 or the wood. 



Salix arbuscula, Whlbg. Bark slit up for 2 inches ; branch 

 1 1 inch thick : otherwise as above. After four days, only those 

 parts directly in contact with the paper reacted ; the salt had not 

 passed beyond in any direction ; the paper was still moist. 



Salix hippophaefolia. Branch 1 inch thick ; bark slit up as 

 in the preceding, but the fluid was actually dropped in on the 

 18th and 19th of June. On the 20th it was found that the 

 solution had not gone beyond ; even the layer of sap-wood was 

 scarcely penetrated Jth of a line deep. 



