164 



upon external conditions of wound-wood formation and of its 

 histology has likewise not been closeljr tested. Undoubtedly 

 the structure will he influenced by nutritive and transpira- 

 tory conditions^ as is that of normal tissues. Compare also 

 the statements on callus page 171. 



The fact that the conditions giving rise to the formation 

 of wound-wood are not only effective, directly at the place 

 of injury and in its immediate vicinity, but also at a con- 

 siderable distance is of great importance, De Vries' e^-p^ri- 

 ments on Sallx, Acer, Evonymus and others (loo. cit. p. 113) 

 prove that, when the outer bark layers are wounded, no wound 

 stimxili are produced, which would ©ause the production of 

 wound -wood, 



Tiseueg resembling Wound-wood . 



Aside from the different forms of gall-wood, to whioh we 

 will return later, there are abnormal wood tissues which do 

 not arise after Injury but from the actiftn of some other fac- 

 tors, These, however, are more or less similar to wound -wood 

 80 far as their histology is conce^rned. Besides these, tis- 

 sues of the same composition must be considered in the follow- 

 ing, concerning whioh no decision has been reached as to 

 whether their production is due t o wound or to other stimuli* 

 We will detote a few lines here to their discussion. 



The production of tissues resembling vround-wood proceeds, 

 as does thp.t of wound-wood itself, either from the normal cam- 

 bium ring or fi^om newly formed, independent cambium. 



Abnormal tissues should be considered first of all, which 

 are produced by the activity of division in the normal cambium 

 ring. In all oases, the deviation from normal histological 

 conditions consists in a lesser histological differentiation 

 of the wood tissue produced. The deviations described above 

 are approximated first ef all when the parenchyma of the med- 

 ullary ray increases in places at the expense of the other 

 formal elements of the wood. Abnormally broadened medullary 

 rays are not infrequently found in fasciated branches. The 

 factors, leading to the fasciation and thereby to the change 

 in histology here named, are still unknown. The occurrence 

 of abnormally broadened medullary rays in non-fasciated 

 branches is also not unusual , 



In other cases normal differentiation is lost to the 

 (183) secondary woody-coalescence in all its parts. As.Sorauer as- 

 sumes^, slightly differentiated wood is produced, for in- 

 stance, in the fruit spikes of Ptrus communis , as a result of 

 rich nutrition and abundant supplying of waier, and as ^ sign 

 of the "weakening of the branches through cultivation". In- 

 stead of libriforra fibres, predominantly parenchjrmatio ele- 

 ments are produced in the wood and generally remain unlifni- 

 fied. Besides these, a luxuriant development of the bark 

 takes place, whioh causes it to rupture here and there. Un- 

 differentiated wood is produced also in the "dropsical" 



Sorauer, (Sorauer), Krebsartige Rindenhypertrophie , 

 Zeitschr, f. Pflanzenkrankh, , 1898, Bd, VIII, p. 220) traces 

 a case observed on Rosa suppositionally back to too rich nu- 

 trition, 



s. <' 



Naohweis der Verwelchljujljwg d, Zweige uns, Obstbaumd 



duroh d. Kultur, Zeitschr, /, pflana^rJ^^rankh, , 1892, Bd. II, 

 p, &6, 



