2o:. 



itive answer can ever bo given to the second question: There 

 is no rpason for surmising any such difference in principle 

 between tro-ture and immature tissues, between chemical and 

 "traumatic" stimuli. It xvould be quite another question, aw 

 to whether the chemical stuffs, furnished by the 'gall-producing 

 parasites, are the ones suitable for inciting the cells of 

 permanent tissues to division. 



It seems to me that a further point must not be overlooked 

 here. If prosoplasmas are produced only from tissues attacked 

 during development, the explanation may lie in the unfitness 

 for use of the permanent tissue, but may also be based,- in 

 some or in many cases,- on the fact alone that the gall animals 

 give out their poison only, to young organs and avoid the old 

 parts. Whether the permanent tissues may p&rhaps be able to 

 proliferate, when it is possible to carry through infection in 

 them, is a question for the solution of which naturally exper- ' 

 mentation is necessary. Unfortunately, however, as is well 

 known, all attempts with experimental cecidiology have failed, 

 up to the present. All my efforts to influence Phytoptes to 

 colonization and to cause them to form galls on permanent tis- 

 sue have miscarried. Still, I do not give up hope of coming to 

 positive results in later Series of experiments, perhaps it IS 

 advisable to make use of organs. Whose tissues are mature, but 

 have also remained tender, so far as their cutioula etc. are 

 concerned, I plan *t some later opportunity to take up again 

 my experiments with etiolated plants or with specimens from 

 moist ciiltures. 



Many galls are produced from completely undifferentiated 

 tissue, from the primary meristem of the tips of shoots or from 

 callus tissue. Many others are produced from organs \yhose tis- 

 sues' already show some distinct differentiation. It is now 

 necessary to make investigations as to whether all t^sue-fqrms 

 of the host plant can furnish material for prosoplasmatic out- 

 growths and further, whether all participate to the same amounj 

 and in the same way in the production of the tissue outgrowtns . 



(229) Prom the outset, cells and tissues with lignified walls 

 are excluded, since, as is well-known, they can not make any 

 further surface -growth. As for the. rest, all living cells can, 

 under certain circumstances, participate in the formtion of 

 galls - no matter if they belong to the epidermis, the ground 

 tissue or the vascular bundle tissue. 



In stem-galls the vascular bundle tissue and especially 

 the cambium belonging to it, often participate greatly J" ;their 

 formatiowi Indeed, many galls of the CyniP^^es winter forms 

 are produced exclusively from the vascular bundle tissue (com- 

 pare fig. 89). In leaf galls the activity of the vascular 

 bundles is less, and often no increaBe of its cells may oe 

 noticed,- rather their development is often prematurely arrested. 



In most cases, the ground tissue produces the largest mass 

 Of gansi pith, bark, and me sophyll often P^jJi^^^^J^f/jSt 

 astonishing lu^rianoe. If, in leaf -galls, t^^ infected part 

 of the leaf attains ten or twelve times the thickness of t^e 

 Sor^l l!af , in almost all cases it is the mesophyll along which 

 has been active. Figirre 96 gives a cross-section through the 

 edge of a gall of Gegid omvia tiliacea . Not only the cells of 

 the assimiXatory tissue ~h£ve been enlarged and strongly in- 

 creased, but even the colorless ground tissue cells,^which^con- 



l'oompare*Ku8ter, Cecidiolog. Kotizen. Flora. 1902, Bd. 

 XO, p: 67. 



