94 RISE OF THE SPRING SAP. 



174 lines (14-5 inches), and therefore exerted a 

 pressure equal to that of a column of water 195 

 inches high. It is quite impossible to account for 

 this pressure by the difference in the amount of 

 dissolved matter in the water absorbed by the roots, 

 and the sap flowing from the cut surface. In the 

 experiment No. IX., of BRUCKE, made with a vine, 

 the sap of which had the sp. g. 1*0009, the mercury 

 was raised at 7 A.M., to the height of 209 lines 

 (nearly 17'5 inches). 



Endosmosis No one can doubt that what is called Endos- 



Utti^share Eiosis has some share in the rise of the sap of the 



L n omeno P n he " maple and birch trees, which is proportionally rich 



in sugar, and differs materially in composition from 



spring water, as well as on the flow or exudation 



of gummy or saccharine juices ; but the pressure 



exerted in these cases cannot be compared to that 



exerted by the sap of the vine, where the causes 



included under the word Endosmosis cannot act. 



The cause It is evident, that the cause of the pressure of 



of the sap the spring sap must be transient, called into action 



by external causes, and limited to a short period. 



Tne experiment of DUTROCHET, from which he con- 

 mfluences. c i u( j es that ftie cause O f the rise of the sap resides 



in the extreme points of the roots, may be thus 

 it exists in interpreted : " The cause of the efflux and pres- 

 the plant, sure of the sap exists in all parts of the uninjured 



plant, down to the extreme spongioles of the root." 

 The present season does not admit of experi- 



ments on this point; but as spring approaches, it 



