6o3 



found at the base of the strong stems of Crimson Ramblers in Germany. 

 Their appearance on the lower part of these rose stems, which, as is well 

 known, grow most luxuriantly in (Germany, reminds one of the same occur- 

 rence in the canker of the grapevine. As in all forms of canker, we find 

 here also that the region of the axis is preferred where branches (A, a) 

 are produced and the base has strongly thickened or split open into curled 

 excrescences {B, iib). As an explanation of this phenomenon, it need 

 only be remembered that the wood ring is broken and especially susceptil)]e 

 to disturbances at that part of the normal axis where a branch starts, for 

 the pith body is widened at the place of insertion of the twig into a pith 

 bridge, transecting the wood ring and passing over into the lateral branch. 

 In such a developing branch the eyes stand closest together at the base; 

 they may often be but little developed, because the leaves are still bract-like 

 or incomplete, but the parenchymatous medullary bridges, which traverse 

 the wood ring, are present. 



The canker spot on the main axis in the present case, as in the "open 

 canker of the apple," shows a central wound surface with an exposed brown 

 wood body (Fig. 142 A and B, w). This surface is encircled by terrace-like, 

 rounded overgrowth edges {n). These wound edges, however, do not 

 retain their uniform wall-like character, as in the canker of the apple, but 

 develop into irregularly knobbed, or beaded, heaped up tissue masses. In 

 other cases, the canker of the rose occurs, like the canker knot in Spiraea, 

 in boil-like, united and elongated wound edges, which line a long cleft, 

 starting from the base of the branch. All excrescent tissues ultimately 

 rupture the bark (r). 



An insight into the production of these excrescences, which are not 

 exceeded in luxuriance by any other canker swelling, is obtained from 

 the above reproduced cross-section of a rose stem, at the place where it has 

 formed a small, isolated bead-like elevation (cf. b^ig. 143). We perceive 

 that the stem has developed normally in the first year; a normal wood ring 

 (A) surrounds the pith body which has broad medullary rays {mst) and 

 which ruptures later (v). In the second year, as the first cell rows {gr) 

 of the new wood ring were in the midst of developing, some disturbance 

 must have made itself felt in the form of some break in the tissue, for the 

 new wood ring {hp), for the most part, has taken on the character of the 

 parenchyma wood and only in places (/?') has it retained the normal wood 

 structure, characterized by the formation of ducts and thick-walled wood 

 cells. The cause of this breaking up of the tissue has been a split in the 

 bark, traces of which may be seen in the lip-like, small indentation at the 

 upper side of the figure. The cork layers {k) of the bark, which cover 

 this, have been split and the overgrowth tissue {zv) swelling out from both 

 sides, which has been covered in turn with a cork mantel, has coalesced into 

 a closed mass in the immediate proximity of the tear (which is not shown 

 in the drawing). If this tissue is traced backward toward the. healthy 

 (upper) side of the branch, starting from the most luxuriant place of 



