209 

 development, the sclereids in the vicinity of the larvae cav- 

 otLJs).''' """'^ distinctly radially. (The Llliri gJ?? anl 



InAP^llcin^t^'^ltrit^'^^ ?^^* ^"^ ^^^^^' ^-^v.elopins r^ore than one 

 nSfnrnl * ^°"? ""^ mechanical tissue, such as those of Cecid- 

 22Zia_qerri6 and very many others, the two mechanical coSts^ 

 are composed of sclereids differing in form. The outer coat 



n«?i= ^v'^'T-'^^' °* ^""l^^ °®'-^^^ °^*^^ elongated like palisade 

 S!;;!^^?^ inner one of arjpreoiable smaller, iso-diametric ele- 



?r*^.i22^^^^® ^^^^^^^ iO^'' ^'^e ^^il^ Jiave to refer later to sin- 

 liar differences. 



(240) The differences in porosity of the sclereids is often very 

 striking. In many galls the ijierahrameQ of the stone cells seem 

 eq^ially closely dotted, the pits standing elose to one another 



' ■inS^^'''i®4...?^ instance, the cynipides galls shonn in figures 

 o» 2^^ A J' ^^ ^^^'^^ °^'^^^' *^^ pitting ia relatively scanty, 

 as ror in seance, in the oft-mentioned beech gall cf Hormoayia 

 ragi - in numerous galls the pitting of the meohanic.il cells is 

 completely lacking, at least in many layers. Ko r>l£ting may lae 

 reoogniged in the upper angular part of the mechanical tissue, 

 in the Interesting (Dipteral gall of Parinariura (Fig. 90);- the 

 oeils of the Icrer, flatly arched part and the s-ccne cells which 

 lie on the under surface of the lead (shaded in the figure) are 

 especially porous. Numerous examples might he cited to prove 

 that the mechanical tissues, which surround the larval chambers, 

 are composed of cells with varying porosity and arranged in 

 zones. The side toward the larvae cavity (figure 105H) is of- 

 ten provided v/ith delicate .sclereids, in which the thickened 

 . . ridges resemble sldnder bands, while in (105E) much thicker cell 



(241) w^lls are met with at si;>me di3t§nce from the cavity. These dif- 

 ferences may be noticed very clearly, for example, in the gall 

 ®^ Qlastrophus Po tentillae. In the fagus-gall (figure 105) the 

 delicate cells of"TFe"~rnn©rmost tissue have pitted walls of a 

 kind similar to that known in the thallus of the Mar chant iaceae. 

 In the Illustration this meshed, most delicate v/all-thickening 

 has been indicated in only a few cells. If an outer and an 

 Inner mechanical coat may, be distinguish®' d, the cells of the 

 first are often only weakly pitted, those of the latter very 

 abundantly so, 



Finally those stone cells must be mentioned, which undergo 

 only a onesided thickening of the walls, thus remaining half thin- 

 walled, or in which the wall-thickening in different parts i* 

 noticeably unequally strong. One-sided or "horse-shoe" thick- 

 ened cells occur under normal conditions, for example, in the me- 

 chanical ring of the laxirineae;- so far as I know, they are com- 

 pletely lacking in the mechanical tissue of the Cupuliferae. 

 Likewise in oak-galls, we find extraordinarily often that all 

 the mechanical cells, or at least the cells of definite zones and 

 layers, are thickened on only one side. In this way the deli- 

 cately walled part of the stone cells in many galls comes to lie 

 toward the outside (Apdricus Quadrilineatus, gryopha nta folii , 

 Br. divisa. Neiir o t e ru s^pimTariT^nd many o the r s , compare figures 

 10'^' aha' 114) 7'Tf^o~af:T'The~c ent er (as in the elliptical gall of 

 the oak, in that of iicraBpis m? cropterae and many others, com- 

 pare fig. 106). It sTems x^rely to happem that the cells, thick- 

 ened on one side, differ also in size and form from the adjacent 

 ones v\rhich have become thickened all around (as in the oak gall 

 shown in figure 107). In all eases in which "horse shoe" scler- 

 eids occur near others thickened on all sides, they form, as it 

 were, a transition to the delicately walled tissue zones. They 

 (248) lie either on the inner etLge of the mechanical coat (figures 



