258 Repoet of the Botanical Department of the 



of growth at different places. These regions of different growth rate 

 vary from 1 to 3 dm. in length and usually of less width, and are 

 irregularly distributed over the surface of such injured trunks. Many 

 maple-tree trunks may be found most anywhere having such irregu- 

 larities of surface. Figure B on Plate XXVII is a rather extreme case 

 while that in figure A is very common. Plate XXI is a section of the 

 same tree taken 10 cm. above that of Plate XX or at point 4 on 

 Plate XXII. In comparing these two sections which are only 10 cm. 

 apart, a striking difference is evident, giving some idea of how the 

 unevenness of bark surface may come about. The regions of ex- 

 cessive thickening in this instance are seen to be due to a sort of 

 double regeneration or growth. As may be seen from Plate XX, 

 the injury occurred when the outermost bark, 5, was still attached 

 to the wood surface at 2; as may also be seen by the line of discolored 

 tissue which makes a complete circle with the exposed wood surface. 

 All the growth between 2 and 5 occurred, then, during the summer of 

 1910. It is evident, too, that in this case the bark and the wood 

 were separated sufficiently by the initial injury to induce the forma- 

 tion of wood tissue and bark on the inner side of the old bark as well 

 as on the outer side of the wood cylinder. At points 1 on this plate 

 the regeneration along the inner side of the old bark failed, resulting 

 in gaps covered by dead bark. In the section taken 10 cm. above 

 this, as shown in Plate XXI, none of the old bark on the left of the 

 figure regenerated, but died. It, however, afforded sufficient pro- 

 tection to the regenerating wood surface to permit that to grow and 

 develop a new bark under the dead one. It seems that the drying 

 effects of the air prevented regeneration on the peeled side. About 

 15 cm. farther up the trunk, on the side retaining the bark, was a 

 patch about the size of a man's hand where there was a total lack 

 of regeneration of both the wood and bark, thus leaving a much 

 depressed dead area surrounded by hving bark. So this gives at 

 least three degrees of difference in the subsequent growth of such a 

 winter-injured tree: places of excessive thickening where a double 

 regeneration occurs, others where the normal rate prevails, and yet 

 others where no growth takes place but where the bark outside the 

 injury dies. 



It seems remarkable that " heart-rot " should have begun so soon 

 after the initial injury: apparently nearly a fourth of the old wood 

 had been permeated by the mycelium of a fungus. On putting a 

 piece of the wood in a moist chamber an abortive fructification of a 

 Polyporus developed on it in a few weeks. A Cytospora was fruiting 

 all over the patches of dead bark shown on the left of Plate XXI and 

 also on the dead edges of bark shown in figure A of Plate XXI. It is 

 unlikely that the mycelium in the wood belongs to the same fungus 

 as that fruiting on the bark. 



The histological studies of such injuries, beginning before growth 

 starts in the spring, and followed far enough into the summer to get 



