158 



injury, the more cross walls are formed. As a result of this 

 the " sltort-celled zone " of the wound-wood is produced near the 

 place of^injury, at a farther distance, transitional forms, 

 which finally pass over into the " j.png>celled zone " of the 

 wound-wood, which is produced frora"undivided cambial cells. 



The cambial daughter cells of the shor^ celled zone pro- 

 duce, near the edges of the wbund5fi a wound-wood composed of 

 polyhedric parenchyraatic cells, whose separate elements gen- 

 erally resemble the cells of the medullary rays in normal v/ood, 

 only a few becoming parenchjrmatio tracheids through character- 

 istic thickenings of the walls. At a greater dlstonce from 

 the wounded surface the daughter cells of the cambium are 

 plight ly pointed to a spindle form , 



In the long-celled zone the cells usually retain the char- 

 acter of wood-parenchyma. Between them narrow vascular cells 

 are produced which are united into cord-like groups; but wood- 

 fibres and broad ducts are lacking. 



After the formation of the elements described, which, with 

 de Vries, we may term t r r ltr.arywound-WQod . there follows, in the 

 short celled zone as welTa-S in the long celled one, a forma- 

 tion of a secondary wound wood . The cells newly produced grad- 

 ually assume a normal form, the tissue regains its normal com- 

 position. This transition is especially worth noticing in the 

 short celled zone; in which the short membered qambial zone 

 must be gradually replaced by the normal long-celled one. Ac- 

 cording to de Vries, a few of the short cambial cells groyj in 

 length thereby crowding upon the others. 



If we areoonaider the histological results as (i whole, we 

 can prove in all cases, in cross wounds as in longitudinal 

 ones, that the wound v/ood remains below the normal so fas as 

 any differentiation of t issues is concerned. The libriform 

 fibres are either entirely absent , or are very insignificant, 

 the parenchyma tic elements advance into the foreground and in- 

 deed so mxioh the. further, the more energetically the wound 

 stimulus acts on the cambium. Concomitant yi^ith the predomin- 

 ance of parenchymatic elements, full of sapj^^the fact that 

 wound-wood is less resistent to injuries of various kinds (frost, 

 parasites > than is firm normal wood. 



De Vries found typical ?/ood parenchjmia in the wound-wood 

 of Caragana arbor escence , although it is entirely absent in 

 (176) the normal Wood Of this plant •^, Still more striking is the 

 formation of abnormal resin ducts in wound -wood, De Vries 

 found that they are of teUpraore numerous in woxmd wood than in 

 normal v/ood, and Voohting*^ proved for Picea excel sa that, 

 reckoned on the surface content, seven times as many occur in 

 wound wood as in normal wood. In fact resin ducts occur abun- 

 dantly in plants which normally do not develop them, for in- 



^ That the elements in question illustrate "real" wood- 

 parenohyma "and have not been produced possibly by cross-divi- 

 sions which had already taken place in the cambial cells, fol- 

 lows on the one hand from the direct observation of the eambium, 

 which lacks divisions at this height", -the long-celled zone 

 of the wound-wood is here concerned,- "and then from the ob- 

 servation, that in exactly radial sections an undivided com- 

 pensating fibre frequently lies on the outer side of such a 

 parenchymatic fibre". (De Vries, loc. cit, p. 24). 



^ Ueber Transplantationen am Pflanaenkorper, 189E, 

 p. 139, 140. 



