184 



a uniform division of the ydojig carabial daughter cells. In 

 my opinion, the occurrence of isolated tracheid-groups favors 

 this supposition. The parenchyma centres f G. .mniperinuml are 

 often followed, toward the periphery, by abnormally short and 

 broad tracheids, furnished on all sides with numerous bordered 



pitSr 



Naturally, a division of the parenohymatic ele- 

 ements and the over-production of a woody-p?,renchyraa 

 , can also occur without abnormal widening of the annual 

 ring. V/oody plants with fungous diseases furnish num- 

 erous examples of this. I wish to mention at this 

 point the production of abnormal resin- canals which 

 are known to be surrounded al'v/ays by parenchyma tissue 

 alone.. Either the number of resin-canals is increased 

 beyond the normal or they occur in wood which normally 

 remains free from them, (cf . the abovesaid concerning 

 wound-wood, page 175) . Hartig^ produced ah increase of 

 the resin-ducts in the diseased places of conifers, in- 

 fected by Agaricus melleus. Anderson^ produced the 

 interesting prooi, "cnat the resin canals are increased 

 not only in the places filled with the fungus mycelium, 

 but in the v^fhole plant, outside the infected areas. 

 (Picea, Pinus, Larix) , 



In Abies pectinata . the v/ood of which is known - 

 to develop no resm-canals under normal conditions, 

 such canals are developed after infection by Phoma 

 abietina even above the constricted place of infection 

 in -fclie xylem, this also occurs in Abies pectinata and 

 Picea excelsa after colonization by Pestalozzia Harti- 

 gii. The abovesaid (p. 17 6) is supposedly true also 

 of the structure of these abnormal resin-canals. 



The transf(l5imation of wood into parenchyma is performed 

 even more energetically by some Zoocecidiae. 



Instead of a formation of parenchyma rays and parenchyma 

 centres, we can prove a production of parenchyma to the great- 

 est extent, in the case of many Heraiptera galls. Just as in 

 the case of callus and v/ound-wood formation, all the cells, 

 or, in the latter, the youngest daughter cells in extensive 

 areas of the cambial mantel divide and furnish a tissue com- 

 posed of isodiametric elements, Vifhile ill the case of injury 

 corresponding to an abrupt interference in the normally con- 

 tinued development of the tissues, the parenohymatic wound 

 (2057 tissue directly joins the normal xylem, we find in the case 



of many galls, that the weak but continuously effective stim- 

 uli given out by the parasites make possible a gradual tran- 

 sition from the normal xylem to a homogeneous gall parenchyma. 



1. Zrankh. d, Waldbaume, p. 13, 



H. Ueb. abnorm. Bildung vo^ Harzebehaltern u. andere zug- 

 leich auftretende anatom, Verand. im Holz erkrankter Koniferen. 

 Forstl.- Katurwiss. Zeitschr. , 1895, Bd. V, p. 439. 



3y Compare Mer, Rech. s. la maladie des branches du sapin, 

 causee par le Phoma abietina. J. de Bot. , 1893, T. VII, 

 p. 364, also Anderson, loc. cit. 



