238 BOARD OF- AGRICULTURE. 



black birch, chestnut, cornel, ash, iron wood, apple and 

 aspen. 



All the trees thus girdled grew through the season as usual, 

 but none of them formed wood below the girdle, except the 

 grape and the red maple. The former, being a branch of a 

 large vine, with foliage both above and below the girdle, 

 formed new wood on both sides of it, and finally, the two 

 callouses were united and communication restored across it. 

 (Figs. 29-30.) 



The red maple, girdled June 23d, formed wood only on the 

 upper side, but the specimen girdled July 21st, formed a 

 new layer of wood and bark upon the denuded surface. This 

 was doubtless owing to the fact that a portion of the cambium 

 was left on the wood sufficient to conduct the elaborated sap 

 and form new tissues out of it. This tree, like the others, 

 grew in the woods, where it was shaded from the direct rays 

 of the sun. The new bark was of a reddish brown color 

 and very smooth, and consisted of a thin layer of periderm 

 or cork, with parenchyma and bast. A drawing of its micro- 

 scopic structure together with one of the old bark on the same 

 tree has been prepared. (Figs. 31-34.) 



There is a popular notion that the bark of an apple tree, 

 removed on the longest day of the year, will be renewed, and 

 it is well known that occasionally such renewal of the bark of 

 various species does occur. This may happen whenever 

 there is deposited upon the old wood enough of the new 

 layer to conduct downward the elaborated sap, and to develop 

 from the living parenchyma of the forming medullary rays a 

 protecting layer of periderm. 



It is not uncommon for the bark of the half-hardy weeping- 

 willow to be started by freezing and thawing from the wood. 

 When this is the case, there sometimes forms a new layer of 

 w r ood upon the detached bark, which is disconnected from the 

 wood of the parent trunk. There is also sometimes formed a 

 new layer of wood and periderm on the old wood under the 

 shelter of the old bark, and roots often descend from the 

 healthy portion of the trunk several feet beneath the loose 

 bark to the ground, and as soon as they penetrate it enlarge 

 rapidly. All these phenomena are readily explained by sup- 

 posing that the liber, or inner bark, of the tree is torn asunder, 



