340 Report of the Hokticulturist of the 



attacked, tliongh the trunks and branclDes of the latter are some- 

 times badly injured, and twigs of the current season's growth may 

 suffer serious injury from attacks of the fungus. Twenty Ounce 

 apple trees are apparently the exception, since in some localities 

 the trunks of this variety are badly injured. The fungus extends 

 down from diseased branches or from canker spots at the forks of 

 the tree till in aggi-avated cases large areas of bark are destroyed 

 exposing the wood in ugly wounds. These patches of black, de- 

 caying wood are conspicuous from a distance. Old age and neg- 

 lect, or a lack of vigor from any cause evidently favor the disease 

 though apparently thrifty trees are frequently ruined by its attack. 



The effect of a canker on a limb depends on the amount of bark 

 that is injured or destroyed. In severe cases the disease' may 

 extend entirely around a limb, thus effectually girdling it. Thus 

 it occasionally happens that the leaves on some part of a tree 

 shrivel and die without apparent cause, but a close examination 

 shows the presence of rough, dead bark somewhere on the limb, 

 indicating the presence of the canker fungus which has extended 

 around the limb and cut off the flow of sap. . 



Plates XXyni and XXIX are reproduced from photographs of 

 typical cankered limbs. In Fig. 1 of Plate XXVIII the character- 

 istic rough bark is shown and at a the wood is exposed, the white 

 fruiting bodies of the fungus, Schizophyllum commune Pr., being 

 conspicuous on the dead bark. At & is a canker spot of compara- 

 tively recent formation. Pig. 2 shows the same limb from which 

 the dead bark has been removed; only a narrow strip of live bark 

 remained that kept the limb alive. Pig. 3 is an enlarged view of 

 the more recent canker shown in Pig. 1 at h. This canker is 

 evidently of three seasons' growth as is indicated by the three 

 series of concentric lines, now rather indistinct, that at one time 

 separated the dead from the living bark. Thie extent of the cur- 

 rent season's growth can be readily distinguished by the smoother 

 appearance, while a distinct line separates the dead from the living 

 bark. 



