207 



layers of thin-^valied cork. Wound- cork is occasionally met 

 with in these galls, in which the outer layers are ruptured 

 by the intensive growth of the inner ones (for instance, in 

 galls of Aulex Hieracii -'-. Lasioptera. 



The f ormation of ba rk is known as yet only in a few galls 

 (Aptera and Eadiois gallsj. (Beverinck loc. cit. p. 64). 



Trichomes . which in structure and arrangement, raav well 

 / nw\ ^®^"^® ^^ ^ protection to the covering tissue in its functions, 

 (207) are not unusual in prosoplasrnas. The gall of Wematus bellus 



(on Salix) bears a thick covering of hair, as aio^fiose "of~Hor- 

 momyia piligera (figure 87) and Meuroterus lanuginosus j The 

 oak galls of Neuroterus lentj,cularis a nd U. numisiaatis -bear 

 heirs Of a striking form, star -like bunches of hairs are found 

 on the former, the single components of which are thick -walled 

 and filled with a brown content; in the others, we find a thick 

 silky hair covering round about the edge of the gall (Figure 

 102a). The hairs of the lenticularis gall are interesting since 

 the bunches of hairs of this stiff, short -membered form are 

 found on numerous Querous varieties, but not on our native ones. 

 The hairy forms of the numismatis gall occur neither on the 

 German nor on any other Quercus variety. They are long, unl- 

 oelliilaar, sharp/y pointed and often two-armed. Both arms differ 

 grestly In length (compare 102c) and are always so oriented, 

 that the longer of the two seems to be centrlfugally directed, 

 the shorter turned toward the central point of the upper side 

 (at a). When studying cross-sections, one cannot suppress the 

 thought that spaclal conditions regulate predominantly the pro- 

 duction of the two-armed forms. To all appearances the hairs 

 (238) become two-armed, because they fill out the space at their dis- 

 posal. At b in the figure, differently formed hairs are shown j 

 some are bent shart5ly, like knees, another kind is bent tivlce 

 and proTlded with a "shsulder" for a second arm. Forms pf 

 this kind andgSlmilar ones are produced only as a result of a 

 laok of space , 



By far the majority of prosoplasmas are naked or only 

 slightly pubeBoent, 



Many galls laok all covering tissue. The galls of Gynlps 

 terminalls on the tips of shoots, produced from callus -tissue, 

 are made up externally of homogeneous parenchyma, the outermost 

 layer not being characterized In any way as epidermis or cork, 

 Moreover, the galls here mentioned belong to those, which 

 "orack open" In places and expose their Inner tissue. In othets, 

 the epidermis is lost inan early st§ge and Is replaced by hypo- 

 dermal layers of stono-calls. 



^ Compare also Skrzlpieta, P., 3>le Axilaaegallen auf Hler- 

 aolumarten. Dissert. Rostock, 1900, 



^ IThlle I traoe the branching of the hairs here described 

 to the notion of spaclal conditions, I assume that even In sin- 

 gle cells the same phenomena of " correlative growth " can take 

 place, as In some organs (for Instance, roots, compare above 

 p. 140). I would like also to trace b^ck to similar conditions 

 the production of abnormally formed trachel.ds in the gnarls of 

 wound -wood, especially the formation of branched forms. (Com- 

 pare figure 70). 



