192 



plasmr.s -xcquires especial interest directly in the gnlls which 

 are slmili.rly formed. In contrast to those discussed above 

 the prosopl?istio leqf- foldings aie set off absolutely sharHy 

 from the healthy pnrt of the lenf fgalls of Pemphigus retrt- 

 £XexuB and others on Flstnola ) . fhe oharaoteristio orescent 

 xorraof the gcll is oonSplououB in the products of Pemphigus 

 eemlltmnlr.rius. Further, ell gclla produced by the aam© ' 

 Bpeoiee are of the nerae size, Plnf~lly prosoplastio leaf-fold- 

 ings, in contrast to those r.bov0 mentioned, shou a p<»oullar 

 tissue differentiation, (Mg. 108 Q,\» 



2, If, through the uotion of any gall poison v^hatever, a 

 Bmll part of the leaf-blade is stimulated to abnorcjally oo- 

 tlve surfaod {:rowth, an outv7ard mrvin^^ of the leaf laase 

 arises, Whether the oarving In this is tipward or downward de- 

 pends aponT7hether the tipper or the under side grows most In- 

 tenelwly. Obviously the slde..T7hioh po-rtloipates in the mo»« 

 active grorrth v/tll beoome convex in the curling back of the 

 leaf. The side growing most is always the one away from the 

 gall animals; the one esiposed directly to the irritation grows 

 relatively little, so that, in this rolling of the infected 

 leaf-area, the gall animals come to lie within the cavity thus 

 produced, PigurenS? illustrates dlagrammatioally the produc- 

 tion 9f this kind of leaf gall. The displaced part of the 

 ^01/ \ ^^^^^'^ Is curvud upwards and encloses,, aft or further growth, a 

 l<Ji4j spacious oaclty, which serves as a dwelling place for the gall 

 animals, r/e term galls of this kind,- sac galls. It is evi- 

 dent thr.t the cavities in which the gall animals here live can 

 not be closed on all sides. An entrance pore always remains 

 open. However, this can be extraordinarily narrowed by sup- 

 plementary grov>fth in thickness of the leaf-mass or may be 

 stopped up By hairs. 



In ciinnection with sac galls we mr.y also recall some 

 earlier statements. Not a fev. forms are found among kataplas- 

 mas in which cavities are formed for the pfirasites by a curling 

 and folding of the leaf, The same is true of aasiny felt galls 

 in which (compare above p, 115) hypertrophy of the epidermal 

 cells conbimes with surface growth of the infected loaf, pro- 

 ducing vesicular projections. In cases of this kind, however, 

 the galls do not hnve the characteristic form and constant 

 size proportions found in prosoplasmas. In them too the "sac" 

 remains very primitive, in aE much as the closing of the open- 

 ing lying on the under side is either very incomplete or does 

 not take place at all. Besides, in kataplastic sac galls new 

 kinds of tissue forms ne'ver occur, 



Sao-galls are produced especially by different kinds of 

 mites, also by Hemiptera (leaf-lice) and Diptera (for instance. 

 C ecidomyia hursaria on (Jleohoma), Their size varies greatly. 

 The leaves of differant maple species are often covered with 

 small, reddish aao-g£T.lls, the smallest of which measures about 

 1/2 ram, in breadth. The galls of the aphis Tetraneura Ulni . 

 whi6h livds on elms, become more than one centimeter large. 

 The pale green sac of Schizoneura lanuginosa (on elas, compri,re 

 fig, 54) becomes severrl centimeters Iro'SQ, The single galls 

 are often spherical, as, for instance, the Phjrtotus galls on 

 the maple. The v;ell -known nail galls of t^e linden are slender 

 and conical, TetraneTira Ulmi produces pocket-like ga3-ls, with 

 sleac'ST bases arid broad ends, Tetraneura cOmnressa (on Ulnus 

 effusa) coxcomb»like sa c-gal Is . SchTzoneura lanugino sa often 

 io bated and knobbed foims. Large sao galls, for instance/ like 

 those formed by Pemphigus marsupial is stand in isolated posi- 

 (215) tions on Iwaares jPopulus) those of g^etraneura Ulroi and others 

 are united into groups of a fow galls, the anail sacs of many 



