CAUSE AND NATURE OF CROWN-GALL 



51 



never observed cells in the process of nuclear division when 

 the Plasmodium was evident, although karyokinesis is frequent 

 in adjacent ones. It may be inferred that invisible cytoplasmic 

 portions of the parasite penetrate the cell walls and pass through 

 adjacent cells to some distance from those in which the Plas- 

 modium is first visible, and that they create a stimulus inducing 

 accelerated growth and cell division. Such a stimulus might 

 also be produced by the effect of metabolic products of the 

 parasite. 



Fig. 26.— Multiuuclear cells from the meristematic tissue of a young gall. (Magnified same 



as scale ; scale = 10 /u..) 



Karyokinesis frequently occurs in large parenchyma cells, 

 even when poorly supplied with plasmic contents, if they be 

 adjacent to diseased tissue (see Plate), and it is presumed that 

 karyokinesis may occur in any normal parenchyma cell and a 

 new center of growing tissue originate under the stimulus in- 

 duced by the parasite. In such cases nuclear division frequently 

 occurs without the formation of a cell plate, and as a result 

 multiuuclear cells are frequent (Fig. 26). Such cells are 

 usually later divided by the formation of walls. 



