PROPAGATION. 



31 



the spongioles, or minute spongy extremities of the fibrous 

 roots,* at which time it consists merely of water, with minute 

 portions of other substances in solution. It passes up through 

 the alburnum or sap-wood, dissolving mucilage in its pro- 

 gress ; it becomes further charged in a very slight degree, 

 and acquires a saccharine character. It ascends to the ex- 

 tremities of the branches, and is distributed through the 

 leaves. Emerging thus from the dark and minute vessels 

 of the wood, it is spread out and exposed to the action of 

 the light, by means of the fine web or net-work of veins 

 ,,, running from the mid-rib to all parts of these broad 

 and thin organs. Here it becomes essentially chang- 

 ed in character, it enters into new combinations, and 

 is charged with the materials for the newly forming 

 wood ; it now descends, not through the sap-wood, 

 but through the inner or living bark,t and deposits 

 a new layer between the bark and the wood. This 

 new layer being soft and fresh, interposed between 

 them, causes that separation known as the peeling 

 of the bark.t 



The sap is capable of flowing sidewise, through 



lateral openings in the vessels or microscopic tubes. 



Hence some trees may be cut at one point more 



than half through on one side, and at another point 



more than half through on the other side, without 



intercepting the upward flow of sap, as in fig. 3. 



Fio . 3i This lateral motion explains the reason why a graft 



set in the longitudinal cleft of a stock, receives the 



sap from the split surfaces of the cleft, and succeeds as well 



as when cross-sections of both are brought into contact. 



* A greatly magnified representation of one of these spongelets is shown in the 



. annexed figure, (fig. 4,) the cen-' 

 tral or dark part being woody, 

 and the point of the exterior being 

 cellular and spongy. 



t The liber, or inner bark, con- 

 stitutes almost the whole bark in 

 young trees, but often not one- 

 half on very old and rough-barked 

 forest trees. 



{ The importance of leaves to 



the growth and even life of the 



tree, is exhibited in various ways. 



j.j ff 4 # A tree stripped of its leaves 



at midsummer, instantly ceaser 



growing. A sue cession of such strippijgs, during the course of tha season, soon 



