144 



extends above the water into the moist air, division takes 

 place *rfT'/ soon in the cambial cella near the upper wounded 

 surf aor'*: » ■ , They are divided "by walls perpendicular to their 

 long axis., producing thereby short prismatic elements. These, 

 for their part, divide in an extraordinarily lively man«B r by 

 forming tangential v;alls, causing an abnormally intensive 

 growth -.in thickness of the cutting near the Injury, although 

 the bark pressure remains unchanged even in these places, or 

 may actually increase as a result of the growtSi in thickness. 



Figure 62 shows a longitudinal section through the upper 

 end of a cutting made slantingly, A powerful callus ring has 

 been developed on its cut surface. The cambium has been in- 

 cited by the Injury to extraordinarily abundant cell division, 

 Not only directly -on the cut surface, but even at a considerable 

 distance belo\7 it, an abnormally lively g'orwth in thickness has 

 taken place,., which acts most strongly at the cut surface, grad- 

 ually decreasing toward the lower part, so that the cutting 

 seems forced out to a club-like form at its upper end. With 

 Th.. Hartig., we can term the wedge thus formed between Xylem and 

 phloem the "Lohden Wedge"^, Above, on the out surface, the new- 

 ly produced tissue fO) Is forced out in a ring-like roll. 



(169) Anatomical investigation shows that, In the production of 



the new structure, the oambial cells have divided just as unf.er 

 normp.l conditions. The Lohden wedge consists of radial rov7S of 

 cells the developmental homogeneity of which maybe seen every- 

 v/here except in the upper cell layers and the convex ring-like 

 roll. In this cell divisions may usualljr be seen in every pos- 

 sible direction but no longer with any regulor arrangement in 

 rows. Sections through very young callus tissue show, however, 

 that no deviation from the normal is present, so far as the di- 

 rection of the first divisions is concerned. The segmented 

 camblal cells divide in a tangential direction parallel to 

 their long axis. Cross walls arise later An the products oz 

 their division and are variouslv oriented. Figure 63 Illustrates 

 *hat has been said. The camblal cells directly at the cut sur- 

 face (B) have perished, those following next have produced some 

 few cells- by tangential division-, the n^xt have divided very 

 abundantly. The arrangement of the products of division makes 

 it still possible to follow the life history. The outer parts 



(160) of these complexes whi^h are formed in rows, - in which cross 



division takes place in very different directions - help to make ^ 

 the outer visible callus roll; their inner parts, adjacent to 

 the xylem, show regular rows with only parallel walls. Of the 

 succeeding cell complexes - at the left in the figure - o»ly_- 

 the inner, regular sections are shown in the drawing. The illus- 

 tration shows at the same time that the cells of the mer Istem of 

 the medullary rays can participate in the formation of the callus, 

 in the same way as do the adjacent segmented camblal cells. 



The next illustration shows in longitudinal section the 

 luxuriant] V develoned "Lohden wedge" (CT of an elm*. The cells, 

 90 ftvjr ce orrongod ic Qlscrpj rooogrlff:* ■&!.«•• t^ve, htb indicated 

 in the figure as curves in the "Lohden wedge". The lowest' (in- 

 nermost) of these curves are bent only slightly if at all, the 

 upper ones (outermost) on the contrary, are bent very stronglyi 

 Since the cells of the "Lohden wedge" not only grow In a radial 



"^ The investigations of the cambial products is made _ 

 easier, if cross-sections are also made on obliciuely cut outtmgs 

 (Compare fig. 62 and 63). 



2 Lehrb. f. Porster, 9 Aufl.. Bd. I, p. 227. 



