194 



(217) the infected part of the leaf. On the entrance pore, however, 

 we find tesides this as a local outgrowth of the leaf-lamina. 

 a rinf-like tissue wall "by means of which the entrance into - 

 the gall-oavity is considerably narrov/ed. According to Prank"^ 

 this orifice -'.vnll is produced earlier thrn the actual sac. 

 Similar conditions e:<;iBt in the case of the mite gall of Salix 

 Qaprea shorm in figure 85B, only here the orlfiee-wall is ex- 

 teneive and fleshy, the sao remaining greatly below it in siz4. 

 The gall animsla remain In the cavity enclosed by the "orifice 

 wall",- they hrvo b.jen "walled in" by the outgrowing tissue of 

 the loaf -lamina. Similar conditions frlso exist in the helmet- 

 llko boooh-leaf gall of Hormomyia fcigi (compare figure 58), 

 Two dovolopmentr.l stages are illustrater'. in figure 86. The- 

 larva, remaining on the underside of the leaf, is "walled-in" 

 (to the Inft in the figure), later the pr.rt of the leaf-lamina 

 which ^.los above it makes an extraordinarily active grov/th in 



(218) HUrfaco and thickness and furnishes the peaked, helmet-llkeg 

 part of the gall, V7hich encloses an extensive larval cavity , 



(to the right in the figure). It is difficult to decide In 

 cases like those described, whether a sac gall or a walled gall 

 is present, However, we v/ill not linger longer over this 

 technical question of subdivision. 



Even the "typiosl", unmistakable walled gells, In 'the pro- 

 duction of Ti^ich no sao formation comes into question, vary 

 greatly among themselves. The oxternrl form as wdll as the 

 nature of the closing of the entrance pore makes possible the 

 recognition of many varionts, Not Infrequently the surrounding 

 walls grow together and complete the closing of the larval 

 cavity, (many Cynipides galls) in others the edges of the roll 

 remain free (many Diptera galls); - to be sure, they lie close 

 upon one another, but do not grow together. Anatomical struc- 

 tures of especial kinds may at times grodiuiio a firm cogging of 

 the contact "surfaces. In their outer forms, the walled galls 

 often resemble spherical, wart-llk(^, or egg-shaped bodies, or 

 conical and bottle-like structures. The latter occur frequent- 

 ly among the products of the Heraiptera (for instance Pemphigus 

 bursarius ) and of the Diptera ( Cecidomyia <;orni and others). 



Wallt?d galls which, in their production, vary somewhat 

 from the tvpe described, are not rare and are often represented 

 in our nature flora. Among the moat striking of these belongs 

 the spirally twisted petiole gall of Pemphigus splrothece , 

 which often Qxtensi\'ely deforms the foliage of poplar trees. 

 At the infected points, the petioles grow out into fleshy, 

 broad bands. wMch twist spirally and finally touch one another 

 on their edges. The contact is so close that a lodging cavity, 

 well enclosed on all sides, is formed for the animals which 

 produce the galls, although no coalescence takes place. 



Finally, the beech leAf gall of Hormomyia plllgera de- 

 serves a special description. While, in the case oj ^n© sac 



(219) and walled galls described above, we have taken i^^Joj^g^^^JJ^ 

 that tissues lying above the infected place - epidermis bark- 

 even mesophyll - can be Incited to (at least approximately) 

 pnnni intpn^lve ffrowth we now find m leaves infected py Hor- 

 mggyla Sifige rg fhnt tfte up?er epidermis can not^participa^ 



"I'xrankh.'d"; Ffl.^ 2. Aufl., 1896, Bd. Ill, p. 54, 



^ Concerning developmental history see especially Busgen, 

 Zur.Blol, d. Galle v, Hormomyia fagi , Forstl.-Katurwiss. Zeit- 

 schr., ,1895, Bd. V, p. ■^' and Ap^el, Ueber Phyto-und Zoomorpho- 

 sen. Wurzburgor Dissertation (Konigsberg 1899 ) . 



