591 



In regard to the juvenile condition of cankered places, I mentioned 

 under Frost Tears that I considered such small tears to be the initial stages 

 of the canker excrescences. In the adjacent picture I give an illustration 

 of two branches in natural size, as I found them on an apple tree, suilering 

 from canker. In Fig. 136 a is shown an oval depressed part of the bark 

 near a bud. The growth which took place after the injury has so in- 

 creased the tension at the dead spot that the dry- bark at its centre has split. 

 At h we see a somewhat further advanced stage. The dead bark in the 

 middle of the wound has already been raised by the overgrowth edges, ap- 

 pearing at the side and united with one another. The places indicated at c 

 and c' in Fig. 136 show conspicuous, protruding knots, with a uniform new 

 bark coxering. At r are the dried scaley, somewhat 

 distended edges of the primary bark of the branch, 

 which has been ruptured by frost. In this, the places 

 are not near a bud ; c is in the middle of an internode 

 and c' on the side opposite the bud. In Fig. 136 i/ 

 t]-!c wound has attacked the tissue surrounding a 

 bud. The bud is dead and the region depressed. 



The wound surface is here very great, the bark 

 /■', under which air has penetrated, is still connected 

 with its healthy surroundings and that newly pro- 

 duced on the edge of the dead spot has caused a 

 widening of the branch, as is very frequent in blight 

 wounds. 



Reproductions of open canker of the apple tree, 

 as well as closed canker, show that the region of the 

 trunk, bearing buds or young sprouts, is preferred in 

 the formation of canker. Such a preference of the 

 region below a short twig is shown in the adjacent 



fie u re of 



small pear branch (Fig. 137). Directly 



Fig. 137. Preference 



shown by frost for 



the base of the 



branch. 



underneath the short twig at a wt find a deep, already 

 overgrown frost tear. At h, the region of the short- 

 ened branch ring w ith its short internodes and many 



weak buds, the bark has been split by many small tears and dried like scales. 

 The young, upper part {c) of the branch has remained healthy. In such 

 bark splits frequently the strongest overgrowth edges are found which often 

 rei)resent a single enclosed knot covered \^'ith uniform bark, but having often 

 two lip-like excrescences touching one another and usually running longi- 

 tudinally. Such wound edges at times appear folded toward the twisted 

 central cleft, the original bark tear, from there falling away ; they then 

 resemble the canker wounds. The bark tears do not always represent 

 longitudinal clefts and, accordingly, the overgrowth does not always occur 

 in the form of two protruding lips but rather as knotty, spherical elevations 

 with a crater-like central depression. On a branch 9 mm. thick, I found 

 canker knots 13 mm. high and 35 to 45 mm. broad. Other branches, just as 



