163 



found occurring in processes of cicatrization and coales- 

 cence ±n the bark , seem to correspond in all essential points 

 with the tracheid groups described above. In them also an 

 independent cambiugi is formed around the core of the wood. 

 The abilitjr to form this kind of isolated wood-cores of larg- 

 er or smaller oorapass might well be peculiar to very many, 

 or indeed to all plants which form wound -v^^ood. 



Tissues resembling wound-wood are produced also In the 

 callus developed from the ground tissue of injured leaves . 

 At any rate, so far as my experience goes, it must generally 

 end with the formation of isolated parenchymatio tracheids in 

 them. More extensive quantities of tracheal elements occur 

 for exnraple in the form of isolated spherical groups of cells 

 in the callus of detached Vicia cotyledons. Here too we find 

 again the formation of gnarls of moderate size. 



Outer gorm and Peri(^d of Development of Wound ^Wood . 



Conditions of its Formation. 



Wound-wood hp.s no definite outer form. Its form is de- 

 termined in the first place by the swollen rolls occurring on 

 the surface of the wound, the form of which depends naturally 

 on the nature of the injury* Shus a differently farmed wound- 

 wood body is produced after cross or longitudinal sectioning 

 than from girdling or spiral wounds and the like. The wound- 

 wood body always adjusts its form to the space conditions 

 granted it. Therefore it is immaterial for our consideration, 

 whether the cambium is incited to the formation of these rolls 

 by injury, by accidental or intentional mechanical interfer- 

 ence with its integrity, or forms them after local injury from 

 frost. If the frost causes the death of the cambium in places 

 of any indefinite extent and if the dead place is later sur- 

 rounded by rolls of wound-wood, then we speak of cank¥r (froSt 

 canker). If the so-called frost tears are caused by a split- 

 ting of the wood, the masses of wound-wood produced by their 

 healing are called frost ridf?es. The manuals of phytopathology 

 give more exact information concerning the significance and 

 distribution of these phenomena ■*■ , 



R. Hoffman^ has shown how the course of the medullary 

 rays in the covering rolls is determined by mechanicgl incidents. 



The period of development of wound-wood varies with con- 

 ditions wnd within wide limits, as does that of callus. It 

 is known that the rolls of "canker" (frost canker) are destroy- 

 ed every winter by the action of cold because of the greater 

 delicacy of their tissues, so that in the following year the 

 injured tree "tries" to heal its wounds by a new overgrowth. 

 (182) Under those conditions wound-wood can be formed for many years, 

 the rolls of which are laid one above the other like terraces. 



The conditions necessary for the formation of wound wood 

 ^Squire still closer investigation, as do those of callus for- 

 mation. As stated above, there hD-s been as yet no successful 

 analysis of the 'Wund-stimuli" effective here. The dependence 



•*■ Ootnpare for example. Prank, Krankh. d. Pfl., 2. Aufl. 

 Bd, 1, p, 207 ff. 



2 Untersuoh, ub. d, Wirkung nechanischer Krafte auf die 

 Teilung, Anordnung und Ausbildung der Zellen etc. Disserta- 

 tion Berlin, 1885. 



