200 



Also the external form of the g&lls very often does not 

 make possihlo conclusions as to the kind of cell divis-:on by 

 which they are produced. Figure 95 shovi's a very earl v sta^e of 

 o$! TH^ ^?^^ ?^ ?^,'^PllieLO:irsarius, which is active on the 



SJ^S rJ'^^^Sr?;? ^''S^^f •■ ^^" ''^°^^ se-ction through the tissue 

 rtog (fj.g, 9bB) a higher magnification shows that the cells of 

 the hark parenchjnna, together with those of the epidermis have 

 heen much divided antiolinally. Hear these my also be found 

 perlciinal walls, which are greatly increased during the further 

 development of the gall. Figure 87 illustrates a young gall of 

 p-?B0S?iO:2_BiliHl^a. Here too a similar tissue ring (a-a) has 

 • been developed, which is iroduced, however, merely by division 

 of the mesophyll cells, parallel to the leaf surface. It is 

 hard to prove isolated anticlinal walls here and there In the 

 tissue , 



(227) The question as to the tissue mgterial . used in the forma- 

 tion of galls, may be considered from several points of view, 



Thomas has thoroughly tested the tissues of plants which 

 produce galls, as to whether they are capable in all stages of 

 life of reacting to the gall stimuli by cell division. His in- 

 vestigations proved that only those tissues. are able to form ' 

 galls which are attacked during development'^. In other words, 

 permanent tissue is incapable of forming galls, 



First of all, to keep to prosoplasmas, no case is known, 

 in which permanent tissue had served as material for the forma- 

 tion of galls* This result is surprising in so far, that in 

 other pathological tissues, even the cells of permanent tissue 

 are found to react to stimuli of differoDt kinds with most di- 

 verse phenomena of growth, I will call attention only to the 

 formation of callus from bark parenchyma which is several years 

 old and from medullary tissue,- to the production of callus on 

 old "ripened" Begonia leaves to the hypertrophy of the bark of 



(228) Gold-ribes, to the formation of tyloses in old wood etc. But 

 what is the condition in kataplasmas, for example, in the bark 

 gall, of the beech-wood louse (Cher me s fagl^?. Har tig's investl- 

 gatioiis (see above p, 207) proveThat, in small trunks which are 

 several yeard old, the bark cells are incifed to proliferation 

 and that the formation of galls can extend even into the wood; 

 thus here old tissue,- permanent tissue- can obviously be 

 brought to excrescence and used for the formation of galls. 



However; it has been emphasized above, that these very 

 galls of the beech woolly louse (compare fig. 79) possess the 

 greatest similarity to callus tissue. Therefore, the question 

 must be asked, are only wound stimuli concerned in the formation 

 of the beech-Chermes-gall, by means of which the permanent tis- 

 sues can be incited to the formation of callus, in the same way 

 as perhaps by girdling, or other somewhat coarse attacks? And 

 further, may the permanent tissues be distinguished from those 

 which have been attacked during development by the fact thgt they 

 can react with cell division to wound and many other stimuli but 

 not to chemiosl ones? I consider it very improbable that a pos- 



^ Compare Thomag, Zur Entstehung der Milbengallen u. ver- 

 wandter Pf lanzenauswuchse . Bot, Ztg, » 1872, Bd. XXX, p* 284, 

 Beob. u'eber Miickengallen, Programm Gympaa. Ohrdruf, 1892, Other 

 investigators arrived at the Same results. Compare Sachs, Physip 

 ol. JJotiaen, 1898, p, 84 (also Flora, 1893, Bd. IiXXVI, p. 241). 

 Beyer in ck, Be Ob. ueb. d, ersten Entwickelungsphasen etc, Idc.cit, 

 p. 180. Appel, loc, cit. p. 52, For the older point of view, 

 compare also Hofmeister, Allg. Morph, d, Gew,, 1867, p, 634. 



