228 BOARD OF AGRICULTURE. 



seems un fortunate that so much has been claimed for osmose 

 in this connection. Boussingault has recently shown that 

 roots containing sugar do not exude it when growing in 

 water, while leaves and fruits, when immersed in this fluid, 

 readily absorb it by an osmotic process and part with their 

 sugar. If the enormous absorption of water by the roots of 

 birch trees, in spring, were accompanied by any correspond- 

 ing exudation, it would appear easy to find it ; but no one 

 has yet detected it. It is not possible to account for the fact 

 that when sap is rising most rapidly, none will flow from a 

 wound in the bark, even when it will run a stream from the 

 outer layer of wood, if the circulation in the trunk is caused 

 by osmose. There is fresh cellular tissue in the liber, and 

 some soluble material, but the bark remains comparatively 

 dry till growth begins. After the cambium has become 

 abundant, why should not all the crude sap press toward it 

 and draw the elaborated material directly into the wood, 

 instead of pushing its way against the force of gravity to 

 the leaves, if osmose is so powerful an agent in the circula- 

 tion ? If this tendency to press into the bark were to exist, 

 there would be a much greater flow from places that are 

 girdled than is now observed ; and probably the bark itself 

 would be ruptured by the pressure exerted, which would 

 often be equal to more than thirty pounds to the square 

 inch. 



One of the most surprising facts to be noticed in examin- 

 ing the wood of any tree with well-developed foliage, is the 

 entire absence of anything like free or fluid water. A 

 freshly-eut surface of the sap-wood is not even moist to the 

 touch ; and if a tube be inserted into the trunk of such a 

 tree, it will frequently absorb water with great avidity. On 

 the sixth of June last, a half-inch tube six feet in length was 

 attached to a stopcock inserted into the trunk of an elm and 

 the tube filled with water. The absorption was so rapid that 

 the fluid disappeared in thirty minutes, and this was repeated 

 several times the same day. Similar observations were made 

 upon white oak; chestnut and buttonwood trees. 



Now the absorption was not osmotic, since the rapidity of 

 it was too great and there was no outward flow, but appa- 

 rently the result of imbibition, or the affinity of the cellulose 



