185 



+v« v*nP! Structural conditions to be stuJLied in the galls of 



l^Ll^T/ .\°^^^.°^ *^e ^PP^^ ^^^ ^^^y Instructive, f Pig. 7 6) 

 First of all. -Che mechanical elements are absent in the ab- 

 normal \7ood; instead of ducts and woody-fibres numerous 

 parenchyite cells are produced by division of the TDrosenchv- 

 raatic elements, which in longitudinal sections show their 

 developmental relation to the regular longitudinal rows. 

 (Fig. 78a) . As shown in the illustration, the single cells 

 have pret-cy thick walls which are pitted. In the layers of 

 gall-wood produced later, the single parenchyma cells are 

 noticeaoly larger while a regular .arrangement is no longer 

 recognizable, and their walls remain delicate, (Compare fig. 

 78b). Ins-cead of normal ducts, only isolated parenchymatic 

 tracheids or others united into groups are formed, distin- 

 guishable from the delicately walled parenchyma cells by 

 their size. Their membrane is pitted like that of a trachea, 

 but often unlignifiedj the tissue structure reminds one of 

 callus. (Fig. 67). In its entirety, the thin- walled woody 

 parenchyma furnishes a soft swelling, wich in water, which 

 can increase to such an extent that the bark is ruptured and 

 the gall tissue laid bare-*-. The fact that the delicately 

 walled woody parenchyma cells are multi-nuclear, as discovered 

 by Prillieux (loc. cit.) is noteworthy. 



The conditions in gills of the beech-louse, ( Lachnu s 

 exsiccator ) are similar to those of the blood-louse. R. Hart- 

 ig'' studied them closely. Here also is found tha same grad- 

 ual transitioji from normal wood to homogeneous, parenchy- 

 matic gall-tissue. 



Abnormal Bark . 



While in many cases (galls of Schizoneura lanigera, 

 etc.) the bark remains practically unchanged, in other gall- 

 formations e^ctensive bark enccresences are produced, v/hereby 

 the changes in tissue, essentially the same as in the forma- 

 tion of woody galls, consist of an abnormal production of 

 parenchjAna. 



The Mycocecidia which should be named here, are pro- 

 duced by Eumycetes and bacteria. 



It is seen in the galls of many Gjnnnosporangium- 

 varieties that the bark and ,-^he v^^ood form excrescences sim- 

 ultaneously. According to Wornle (loc. cit) , in weakly 

 grown branches of Juniperus communis, Gymnosproangitim clava- 

 riaeforme incited the bark rather than the wood m a tissue 

 production. Hand in hand with the superabundant formation of 

 parenchyma, proceeds an arrestment in the formation of the 

 parench^nnatic, mechanical fibres. They remain thin-walled 

 and decrease in number. Therefore in a comparison of normal 

 with abnormal barks, essentially the same points of consid- 



1. Prillieux, etude des alterations prpd. d. le bois 

 du pommier par les piqures du Puceron langiere. Ann. Inst. 

 Hat. Agronom. , 1877, T. II, p. 39. 



2, Die Buchenbaumlaus (L achnus exsiccator Alt. ) Unter- 

 such. aus d. forstbot. Inst, Munchen, 1880, Bd. I, p. 151. 



