165 



branohes of Rlbes^^tror.ted of earlior, Still more examples 

 of this kind might be etted; an arrestment of the processes 

 of differentiation and nn increase of the parenchyma con- 

 tained in the wood is almost nlrrajrs assooiated with over 

 production of wood. 



Those cases mnst still be mentioned in which now oam- 

 blal layers are produood, leading to an abnormal formr.tion 

 of V700d, Just r,s in wound tissues described above, isolated 

 wood cores of varying size are produced by the activity of 

 their division* 



Sorauer has given thorough anatomical descriptions of 

 the "tuber-like gnarls" of the stone-fruit trees, and Kriok 

 of similar formations In beech bark^, 



Sorauer found tuber-like woody bodies in the bark of 

 Plrus malus . In their centres lay one or two hard bast bun- 

 dlGS, separated by lignified parenohjnna. About these "are 

 layered in a ray-like arrangement, first of all approximate- 

 ly iso-diametric cells of wSod parenchyma, lying bluntly up- 

 on one another, and usually oontj?aining starch". Little by 

 little this zone passes over into narrowef, thicker-walled 

 wood parenchyma cells, already somewhat elongated and running 

 horizontally or diagonally^ between them are scattered short, 

 bro&d simple pitted duct cells. These groups have already 

 been divided Into numerous circles of bundles by approximate- 

 ly cubical medullary ray cells, lying possibly from 1 to 3 

 rows thick. The further the celleelements are separated from 

 the centrum, the more marked is the difference betvTeen the par- 

 enchyma of the medullary rays and the elongated fibro-vasou- 

 lar tisjsue. Weaii the centrum, begins also the phenomenon 

 which makes itself felt throughout the whole wood body, th?xt 

 is divided Into different annual rings,- viz., that the ele- 

 ments of the fasciated partlying between two medullary rays 

 show a different course than do those of the parts lying near 

 it. While the razor cuts through the cells and iucta of one 

 bundle almost in cross section, it strikes those of the adja- 

 cent bundle longitudinally". Many tuber-like gnarls vary from 

 these here described, in that the hard best bundle is lacking 

 as a centrum; Instead of this is found a group of bark paren- 

 chyma cells. 



The Isolated wood bodies s which Sorauer (loc, cit, p. 185) 

 found in a branch of Pirus communis resemble in all essential 

 points those described, - in which a one-sided flat swelling 

 was conspicuous, "2?h© cross-section through the middle of the 

 (164) swelling showed new, isolated, wood bodies almost touching one 

 another, however, at the sides, which were entirely separated ^ 

 from the central wood cylinder of the branch by a normal cam- 

 bium and secondary bark zSne. Each of these wood bundles bore 

 in the center a hard bast group and had also the structure of 

 the centrum of the tuber-like gnarl of the apple, only, the 

 wood cells and ducts were not arranged cone-like on all sides 

 about the centrum but extended parallel to the length of the 

 branch. There were, therefore, no wood tubers, but short 

 wood- cords, which traced further downwards became steadily 



1 Sorauer, Wassersucht bei Ribes aureum , Preihofffs 

 Deutsche Gartenzeitung, 1880. 



^ Sorauer, Die Knollenmaser der Kernobstbaume, Land- 

 wirtsch. Versuchsstat., 1879, Bd, XXIX, p, 173, Handb. d, 

 Pflanzenkrankh. , 2. Aufl., 1886, Bd. 1, p. 7S6. Krick, Ueb, 

 d, Rindenknollen d, Rotbuche. Bibl. Bot,, 1891^ Heft ^5. 



