18 



THE FOOD OF TREES IS IMBIBED 



PT. II. 



herbaceous envelope. Or, at least, tliey are equivalents 

 to what would bear these euphonious titles above 

 ground. Continue to break off small pieces of the 

 root. A third tube will be found, — a ligneous thread, 

 ending in the finest point, and growing gradually 

 thicker. The thread being comparatively tough, the 

 outer coatings may be pulled off it for many inches. 

 The internal thread is the wood, and is the conduit for 

 the ascending sap which approaches nearest to the 

 extremity of the root. The external coatings are the 

 bark, and the inner bark is the conduit for the de- 

 scending sap, and the means of the growth of the 

 root, as well in elongation as in diameter. 

 Ends of The silver ends of roots are, in fact, a mere pro- 



bark,which lonc^ation of the bark, without wood. Down the bark 



is the des- 



cendmg, all physiologists allow a descending current, but none 

 conduit^"' allow an ascending current. I believe, indeed, that 

 there is a power of absorption and of lateral transmis- 

 sion of moisture across the bark into the wood, and 

 that the layers of wood are the upward conduits for 

 the sap. But if we suppose the possibility of the 

 absorption of moisture by the immature and silver 

 ends, we cannot suppose the possibility of its trans- 

 mission upwards, where there is no wood, but only 

 unripe bark in process of formation and deposition 

 from above, which bark, even when ripe, is the descend- 

 ing, not the ascending, conduit ; and though on extra- 

 ordinary emergencies the sap may for a short distance 

 flow up the downward conduits of the bark, it is rather 



