255 



There remains finally a coriparative consideration of the 

 fat© of the different tissue forms,- epi£»ermis, groiind tissue, 

 ■vasculp.r •hundle tissue. In this v/e rill limit ourselves to 

 vascular plants. The above-said holds good so far as the util- 

 ization of galls in general oonclusions is concerned. 



1« Epidermis 



The epidermis proves itself in general pretty resistant to 

 arrggtinit»: Iftfluenoes . In oulttireg in the dark, in moist places 

 etc, its composition of histologically different elements re- 

 mains approximately nerraal. To b e surd pubescence is more or 

 less reduced in the onltures mentioned, but the storaata are al- 

 most nlT7aya retained, Oauohery proved in dwarfed plants, that 

 the size of the epidermal cells remains normal in almost all of 

 the 3p©»les intestigated. 



The epidermis le easily susceptible to favorable influences . 

 It is possible, under yery different kinds of cultural conditions 

 to produce abnormally Irrge epidermal cells. In ctiltures in 

 moist plaoea, o fter infection by fungi etc., we find a produc- 

 tion ol abnormr.lly large epidermal oellsp- even the guard cells 

 can attain an abnormal size (fig. 16). Callus hypertrophy of 

 the epidermal cells, of v/hlch the guard cells are also capable, 

 is Illustrated in figure 2«, Instances may also be found among 

 Intumesoenoes In which the epidermal cells have become abnor- 

 mally enlarged (Fig, 22), Eap©cla^5.y interesting is the fate 

 of the epidermal cells, which are Incited liy gall mites ta hy- 

 pertrophic gror/th, growing out to extensive, almost always uni- 

 cellular pbuches differently formed, fPigs, 38, 40). 



\7hen considering abnormal cell-division tn the epidermis, 

 we must distinguish between divisions perpendicular to the 

 upper surface of the plant organ concerned, and those parallel 

 to this surface. ^ 



In the production of many galls, we find that extensive 

 ©xoreacences arise by outgroi^th of the gro-and tiSv^ues which are 

 covered on all sides by epidermis. In this case, the epidermis 

 fE9T) follows the growth of the gall-struotare by rspeated division 

 perpendicular, to the upper surface of the organ. It can not be 

 stated definitely,, whe^bher the cells are Incited to the pro- 

 ceases of division only by passive distention or by the gall 

 poison. That the epidermal cells are actually acted upon by tm 

 gall poison, hewever, and influenced by it, is proved by the aV 

 iicrmai hairs which often grow out of its cells at the infected 

 spots'^. 



Division parallel to the upper surface is rare. Only In a 

 few galls do we find a many layered epidermis formed from the 

 normal one-layered one ( Spathegaster ba ccarum, Uematus etc.). 

 Compare figures 98 and 9^, and in sdme~Inl?5mo see noes (see above). 

 But even where cross-division does take place in the epidermal 

 cells, it occurs less frefiuently than in the groimd tissue cells 

 belonging to it. The Same holds good in the development of all 

 callus formations, Th't epidermal cells maybe incited oorrela- 



In many oases the epidermis is not able to follow the 

 distension of the internal tissues by surface growth, I call 

 attention to the gall of Hi>rra onyla p: ai:>!^ra (fig. 87) the 

 Jaoquinla gall (fig.loi) and" many Jntumescences (fig, 20). 



