. OA. 
. 
4 
* 


On the Mechames of the Ascent of Sap in Trees. 463 
against the osmotic attraction of the dissolved salts; while the maintenance 
of equilibrium along the vessels of the balanced osmotic column, with its semi- 
permeable partitions, demands that an equal amount of water must rise 
spontaneously to take the place of what is thus removed. 
The subject might, perhaps, be further elucidated by observation of the 
manner in which the flow is first established at the beginning of the season, 
or possibly by experiments on the rate at which water would be absorbed by 
a wounded stem high above the ground. 
