210 



106 and 107), or on both this and the outer edge, furnishing 

 both the transition and the soft parenchyrap. (Fig. 114). Dn 

 the other hand, galls are found, in which stone cells, thick- 

 ened strongly on all sides, directly follow the delicately 

 walled parenchyma. Figure 119 shoua finally that oven complete- 

 ly isolated zones of sciereids, thickened on half their sides, 

 may occur. It iP a mrtter of course, that this thickening of 

 only half the sides d&es not exdludo the formation of pits. In 

 the gall of Oynips l if^n^cola and many others, the thickened 

 part of the wall is 'For 5 strongly pitted, IVe v.dll have tor^e- 

 port later on the remarkable phonoraenrv of secondary growth, 

 vrtiioh has been verified in many of the scloreids of Cynipiaes 

 galls, the walls of whioh have boen thickened on one side. 



Unequally thickened aolereidsg, the lumina of which show 

 bottle-neck, pointed forms occur in various Oynipides galls. 

 Compare fig. lOf, also fig, 114), 



The OQlls in the gall products of other insects fStefani- 

 ella Tri naoriae on Atriplox and ethers), v;hioh are thickened un- 

 equally or orTHalf their sides, are rarer and less striking 

 than those of the Ojmipides oak galls, 



243) 11. Having discussed the qualities of the individual me- 



ohanioal cells, it v/ill be necessary to investigate the way in 

 v/hich Binglo cells are united into mechanical tissues and what 

 may be the distribution of the mechanical tissues inside the 

 gall body* 



In most cases the mechanical cells of galls combine into a 

 close mechanical tissue, Wot infrequently, however, a soft par- 

 enchyma may be found within this in which isolated stone cells 

 are scattered (compare figure 101). The manmr in which the 

 single, thick-walled cells join on t6 one another, diwsplays noth- 

 ing unusual: either parallel rovrs are produced (as in figures 

 90 and 95) or irregular bands. Small intercellular spaces be- 

 tween the simple nclereids are very clearly recognizable. In 

 order to be able to describe the arrangement of mechanical tis- 

 sues in the gall body, reference must be made to the other tis- 

 sue forms. in galls, 



Laoasse-Duthiers (loc, ci<5, p. 292), on the basis of his ob- 

 servations on highly organised galls, siich as those of Cynips 

 tinltoria and others, differentiated the following tissue layers: 



(.1, epiderme . 



(2, tiSFUG oellulatre sous-epidermique 



I. (3. parenchyma (spongieuse 

 ( (dure 



(4, vaisseaux 



II. ( 5, couche protectrice 

 ( 6. partie aliment aire 



Beverinck (loc. cit. p. 39). called the ^^^^J'^^^^^f ?4j^'^i^^^^ 

 (ID "the inner gall", the others (I) all together the gaii oarK 



The different formation of the couche protectiice, in con- 

 trast to gall bark, makes possible' the differentiation of the 

 following three types in mechanical gall tissues. 



I. The mechanical tissues lie comparatively deep in the 

 Inner part of the gall. An epidermis and a bark ^Jf^^^^^f.^^^"" 

 walled parenchyma is present which can differ greatly in thick- 

 ness and histolggy^ 



