REACTION OF THE PLANT. 



shallow, no gall results. In the crown-galls, growth may begin, it would seem, in the inner 

 wood, in the cambium ring, in the outer bark, or in the mesophyll of a leaf, i. e., wherever 

 cells are naturally dividing. The division of cells may take place so rapidly that all or a 

 large part remain small. The earliest stages of the tumor formation have not been traced 

 in serial sections. Soon more definite information will be available. 



In sections of young crown galls mounted unstained in sterile water small clumps of bac- 

 teria may sometimes be seen inside of unbroken cells and moving granules and rod -shaped 

 bodies in small numbers some of 

 which have appeared to be self- 

 motile, the longer ones flexuous and 

 occasionally one constricted in the 

 middle, but stained slides have thus 

 far given no clear-cut pictures. 



HYPERTROPHIES. 



In hypertrophied tissues the in- 

 dividual cells are larger than normal. 

 Usually bo thhyperplasia and hyper- 

 trophy occur in the same growth, 

 e. g., in olive-tubercle. Good ex- 

 amples of hypertrophied cells occur 

 also in root-nodules of Leguminosae. 

 Here their volume may become 

 many times that of the normal cell. 

 Hunger pointed out that tyloses 

 are very common in the vessels 

 of plants attacked by Bact. solana- 

 cearum, and ascribed their forma- 

 tion to the presence of the bacteria. 

 Of the correctness of this view I 

 have since satisfied myself. The 

 writer has seen the same thing in the 

 wood of young shoots of the mul- 

 berry attacked by Bact, mori (fig. 

 30). Here the stimulus to growth 

 appears to be due to poisonous 

 products absorbed by the vessels 

 of the plant in advance of the move- 

 ment of the bacteria. This is quite 

 in accord with what we know 

 of the action of many poisons, 

 minute doses stimulating and larger 



doses destroying. The formation of tyloses in the manner described raises the question 

 whether they may not be formed often under the stimulus of absorbed foreign substances, 

 e. g., in the roots of old cucurbits where they are very abundant. Various attempts were 

 made by the writer to stimulate their formation in roots of young cucurbits by addition of 

 ammonia and ammonium acetate but thus far with inconclusive results. The tyloses 

 sometimes appeared within a few days, but small numbers of bacteria also occurred and 

 may have been the determining cause. Only when we are able to obtain them promptly 

 without contaminating bacteria can we be certain. 



Fig. 27.* 



*FiG. 27. Swelling on a potato shoot inoculated with a non-virulent culture of Bact. solanacearum (Va.). Plant 

 118 inoculated Apr. 16, 1904. Photographed May 25. Disease at an end. 



