797 



adjoining the old wood (Fig. 183,5:' to S), as its innerside, in contrast to 

 the spherically convex outer side, the parenchymatous tissue of the inner 

 edge, lying directly under the cork zone, is seen even in the second sections 

 to color more deeply when treated with iodine than does the corresponding 

 part of the opposite outer side. In the same way, by using iodine, a radial 

 division of the tissue may also be recognized, for certain bands at first only 

 one to three cells broad take on a deeper color than the broader parts lying 

 between them. A difference may be seen also in the form of the cells in the 

 first cross sections, for those lying nearer the outer edges appear rounder 

 than the more densely crowded ones nearer the inner edge ; also all the cells, 

 lying directly tmder the corky outer layer, are smaller than those at the 

 centre. The lighter colored bands contain cells with a greater radial elon- 

 gation, the first indication of the medullary rays. The zone of the renewed 

 cell division, which will form the beginnings of the later cambial rings, 

 lies close to the inner side of the callus roll adjoining the region of cells 

 which were the last to divide to strengthen the peripheral cork zone. From 

 there, in the subsequent cross sections, the division zone moves farther and 

 farther from the old wood (compare the curved course in the longitudinal 

 section, Fig. 183, c to c'), reaching its greatest distance from the old wood 

 outside the plane in which the girdling occurred and again within the old 

 bark, approaching the normal wood until it takes up the usual position of 

 normal cambium. 



The principles that have been discussed here in detail with reference 

 to the grape are expressed in any kind of girdling, the special structure 

 naturally varying with the kind of plant. 



Czapek^ has shown that, of the conducting elements, only sieve tubes and 

 cambiform cells come under consideration for all assimilating products, 

 indeed, the paths which convey substances are straight, even in the phloem. 

 The phloem parenchyma, like the medullary rays, serves as storage tissue. 

 The deposition of reserve substances is influenced by girdling, inasmuch as 

 (according to Leclerc du Sablon-) the roots of trees girdled near the base 

 of the trunk in the spring at the time of sprouting are richer, and the trunks 

 poorer, in reserve materials, than those of trees which have not been girdled. 

 The leaves of the former to be sure are not so green, but contain much 

 more reserve materials than ungirdled specimens and according to my obser- 

 vations color much earlier in the autumn. 



Injuries to the Bark. 



A. Historical Survey. 



The processes of healing a wound which has exposed the wood all the 

 way around the trunk often a meter in width, produced by the removal of 



1 Czapek, Fr., tJber die Leitungsweg-e der org-anischen Baustoffe im Planzen- 

 korper. Bot. Centralbl. 1897, Vol. 69, p. 318. 



2 Leclerc du Sablon, Recherches physiologiques sur les matigres de reserves des 

 arbres. Revue generale de Bot., Vol. XVIII; cit. Bot. Centralbl. v. Lotsy, 1906, No, 

 43, p. 447. 



