Mechanloal Tissue 208 



We villi tG3-m mechanical tissues those whi*h are conposed of 

 stone-cells. This name If? justified by the fact that ?/ithout 

 doubt the layer of stone cells can 'act mechanically because of 

 its firmness.. The larval chambers, which are composed of mechan-- 

 ical tissues, and thoir inhabitants are thus shielded from pres- 

 sure and blo7;s - and protected from the attacks of animal endmics. 

 Lsoasse-Buthlers, v/ho had recogni55ed this community character of 

 the stono-eell tissues in galls, termed the firm aone a "couche 

 proteotrice". 



Compared ¥7ith the formation of oeohF.nioal tissue in the nor-^ 

 mal plant body, the strongthoning tissues of galls mr.y be of tv/4 

 kinds: cither the gjills carry over their mechanical tissue from 

 the plssnt organ, which produces thorn, or thoy produce a tissue 

 of this kind for themselvoB. "A Pathological Anatomy? Is natur- 

 ally concerned only v-ith a study of the latter. 



The "externcl" galls only rately lack all meohnnical tis- 

 sues as in the different nematus varieties on the willow. VTe 

 find in most g£.lls an extraordinarily rich production of stone- 

 cell tissues. We uill study first of all the qualities of the 

 elnglcj. thick-walled cells and later the form and distribution 

 of mechanical tissues, 



^ 1. All thick-wallffd cells, found in galls, are sclerelds. 

 Sclerenchyma fibres (storeids)na»e absolutely lacking in galls. 

 The amission of the prosenchymatic mechanical elrfinontr, ccnf-orm& 

 with the parenchjmr.tic character peculiar to all gall tissues 

 and also to callus formations. 



Within the boundaries drai.7n for the forms of the mechanical 

 cells by their strongly retained scleroid-character , v/e find 

 nevertheless an abundant variation. The form of the stone cells 

 (239) differs greatly In the different galls; their porosity and the 

 degree of lignifi cation are also unequal. Finally, the stone 

 cells are very noticeable, v/hlch are produced by the unequal 

 grov/th in thickness of the cell -membranes. 



In the majority of cases the stone cells of the galls are 

 small, round, and Iso-diametrlc, as shown in figure 93 (Banls- 

 teria gall). In other galls, however, we find ahgular cell forms, 

 stretched like palisade-cells and usually oriented perpendicular 

 to the upper surface of the gall body, similar to the rod-like 

 sclerelds of many fruit and seed shells. Figure 103 gives the 

 cross-section of a gall of Hormomyla fagi . The greater part of 

 the gall tissue is composed of elongated, thick-walled cells, the 

 walls of T^hlch are much pitted. Here and there little intercel- 

 lular spaces have remained free. Elongated sclerelds, with a 

 distinctly radial orientation, are found in the galls of Oynlps 

 kollari G. tlnctoria and many others. Occasionally palisade 

 sclerench2TtiP. is produced forthwith in young galls by sclerosis 

 of the asslmllatory palisade cells, or the cells of the latter 

 become enlarged before they have hardened to gall -parenchyma. 

 The oak gall of Gecldomyia Gerris (figure 104) may serve as an 

 esample of this case. 



Even when the cells of the mesophyll divide abxindantly, 

 their derivatives often retain the form of typical palisade 

 cells (for Instance, in the gall of Geoidomyia tiliacea ). Ii 

 thev have hardened near the gall-cha.mber into a "coucne protec- 

 trlce", we find it composed of palisade cells all oriented par- 

 allel to one another. In galls having a different process of 



