OBSERVATIONS UPON THE PHENOMENA OF PLANT- LIFE. 333 



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. 



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 occasion- 

 ally 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 paren- 

 chyma 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 Avood. When this is the case, there 

 sometimes forms a new layer of wood upon the detached bark, which is dis- 

 connected 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 en- 

 large rapidly. All these phenomena are readily explained by supposing that 

 the liber, or inner bark of the tree, is torn asunder, a portion sojietimes re- 

 maining attached to the wood sufficient to conduct the elaborated sap, and so 

 form a new layer of wood with a layer of bark. The roots are developed from 

 the uninjured portion under the protection of the old bark, and in their nature 

 are precisely like roots from cuttings. 



EFFECTS OF FROST. 



The rupture of the medullary rays and the separation of the bark from the 

 wood by the combined, action of frost and sunshine is not uncommon in the 

 apple and other cultivated trees. If a severe frost separates the water from 

 the wood as ice, and it then thaws and freezes again before it can be absorbed, 

 it will be likely to burst the bark or tissues in which it is accumulated. This 

 usually results in one or more cracks through the bark on the southerly side 

 of the tree, from which there is, in the case of the apple tree, commonly a 

 slight flow of crude sap in the following April or May. The outside of the 

 bark is blackened, and the detached portions die. 



In the spring of 1874, a vertical crack three feet long was noticed in the 

 south side of a vigorous young Gravenstein apple tree in Amherst, the trunk 

 of which was about three inches in diameter. Upon examination, it was 

 found that the bark had not been separated from the thick layer of wood 

 formed the previous year, but that this outside layer was entirely detached 

 from the wood beneath. The bark, being supplied with sap ascending through 

 this layer, remained sound, and the crack having 'been filled with wax, the 

 tree grew equally well with others in its vicinity which had sustained no in- 

 jury. The new growth on the sides of the crack being covered only with a 

 thin, soft periderm, will doubtless readily unite, and there will soon remain no 

 trace of the rupture. The separated layers of wood, however, will never be 

 reunited, though the inner ones may conduct sap, until converted into the 

 nearly impervious heartwood which occupies the central portion of every 

 trunk after it attains to any considerable size. 



At what age, if ever, the inner wood of exogens loses all power of conveying 

 sap, and whether the sound heart of an old tree which has never been ex- 



