162 



centricnlly layered bark tissue with abundant latex tubes. 

 The sq^arate balls are usually connected with one another 

 ^nd with the cambium of the cutting by means of cambial 

 bridges. 



The cases here described prove at the samt time that 

 the formation of the balls is not connected with advanced 

 fr^?.^ i" !^® production of wound wood, but nmy also indicate 

 the beginning of its formation. 



Tissues furnishiilg wound -wood 



Just as the oambium, to the derivations of whieh the pre- 

 ceding statements chiefly refer, can produce woxmd wood or 

 products similar to it, all other tissues, furnishing callus, 

 can also produce wound wood under certain circumstances. The 

 P^^h is concerned here more thSn all other tissues, Jn differ- 

 ent plants, for Instance in Populus, it is highly capable of 

 forming callus. In the medullary callus, tracheids and groups 

 of tracheids are also produced very early, on the periphery 

 of which are formed new meristematic tissues. The formation 

 of tracheal elements which PrillieuxMtudied in the pith of 

 different cuttings (Coleus, Ageratum, Aohytanthus and others) 

 should be mentioned* 



Ml 



A case described by Maule (loc. cit» p, 27) is of inter- 

 est for several reasons. In Evonymus europaea . cambial forma- 

 tion was brought about in the pith when it had not been direc- 

 tly injured. In several branches, from which rectangular 

 pieces of the bark had been cut the cells of the round tissue, 

 resembling parenchyma and containing chlorophyll, which lies 

 between the pith zone ®nd the pith, was incited to division 

 beneath the place of injury. From the new tissue thus pro-- 

 duced, a cambium wqs differentiated which, extending }ikean 

 arch, produced xylem on the inside, phloem on the outside, also 

 a new bark zone and q new cork layer, "so that therefore, all 

 the zones of a regular woody-trunk are formed within the old 

 woody body". "It must still be noted that the beginning fef 

 the formp.tion of wound -wood in the pith did not coincide with 

 the beginning of its formation on the external, directly in- 

 jured, part of the branch. As a result of the exposxiro, the 

 wood under the places v^^here the pieces of bark has been re- 

 moved, began to turn yellow, i. e, to be changed chemically. 

 This change progressed slowly towards the oenterj especially 

 along tho medullary ray until the entire old wood body had 

 been altered as far as the injury extended. If the transfor- 

 mation in the medullary rays had penetrated as far as the pith, 

 cell division then began in the latter. There existed here 

 therefore the remarkable case, that the pith was not directly 

 brought to the formation of wound-wood by the injury, not even 

 by the wound stimuli, but only by a secondary phenomenon' con- 

 nected with the injury". We will later find other cases, 

 (181) which make it seem probable that living elements adjacent to 

 the dead cells can be stimulated to division by the products 

 of decomposition in the latter. 



The isolated wood bodies, which Vochting and others-*- 



•*• S, 1, formetions ligneuses qui se produisent d. la moelle 

 d. boutures. C. R. Acad, Sc, Paris, 1882, T. XCII, p, 1479. 



2 II 



Vochting, j^oc, cit, p. 141, 142. Tschirch, Pflanzena- 



tomie, p, 396, Maule, l)er Faserverlauf im Wundholz, Bibl, 



Bot., 1895, Heft. 35, p, 23. 



