791 



like arrangements of pits corresponds to the pores of the cells surrounding 

 the ducts in rows, the walls of which cells are pressed against those of the 

 ducts. 



The lower cut, by which the ringed place was laid bare (Fig. 182 bl) is 

 indicated in Fig. 183 by the plane S,S'. In this longitudinal cut, therefore, 

 the girdled exposed surface extends from vS upward along the exposed wood 

 cells. At S', we see how the knife has smoothly cut the bark (R) perpen- 

 dicular to the longitudinal diameter of the vine. At the time the cut was 

 made, the bark (R) lay close against the wood (H). The tissue lying 

 between them and projecting far out (r,C,C') has been produced after the 

 girdling. And, indeed, the extreme lessening of the bark pressure con- 

 nected with the removal of the bark in the sectional plane SS' and the parts 

 adjoining it in the cells of the cambium, as well as in those of the youngest 

 wood, likewise in those of the younger and youngest bark, causes a forma- 

 tion of callus with a surprisingly great cell increase, since the end cells of 

 the tissues named and those directly adjoining them push outward, divide, 

 elongate and cut off their anterior ends by cross walls. In these anterior 

 ends, the elongation and construction is repeated many times. In this way, 

 a callus wall (C,C') projects in a circle, around the cut edge of which the 

 inner side at s' lies close against the wood, without uniting with it. 



At any rate, this callus wall at first has neither the extent nor the 

 structure given it in the drawing; this represents rather a wound wall devel- 

 oping from the callus which, by the increase of the new cambial zone (c), 

 has already formed secondary elements of thickening. Originally this callus 

 wall consisted only of thin-walled parenchymatous cells (s,s') appearing 

 immediately and radially arranged, their diameter in all directions being 

 almost equally long. 



In such a juvenile callus wall, which is early differentiated, a cork zone 

 is formed (k,k"') first of all on the outer circumference. It gradually 

 increases in thickness and serves as a layer protecting the thin-walled, 

 newly formed tissue mass. The cut surface of the old bark tissue (R) 

 which has been separated widely from the wood by the new wound tissue, 

 is cut off in the same way by the cork layer (k"). The old, hard bast cells 

 (b), which have been cut, have turned brown from the cut surface deep 

 down into the healthy tissue and died. The original bark tissue (r) lying 

 inside and back of these bast cells has participated in the cell increase and 

 callus formation; only the cells lying next to the hard bast of the original 

 bark have formed a cork zone (k" '), cutting off the dead part. Near this 

 cork zone run the hard bast cells (&'), which were already formed at the 

 time of girdling, but under the influence of the cut do not extend normally 

 as at b. The elements of these cells arranged in rows may be traced back- 

 ward into the healthy tissue and gradually pass over into the old bast;' this 

 row of cells is continued in the wound wall in the elongated, but very thin- 

 walled groups of cells (b"), which lie at equal distances from the cambial 

 zone. 



