460 BACTERIAL DISEASES OF PLANTS 



Is it really a growth from the primary tumor, in the sense of a 

 pushing in between tissues or only a change in more and more 

 distant cells owing to the propagation of a chemical stimulus? 

 Sometimes it would seem to be the one and sometimes the other. 

 If the cells of the tumor do not change position, how do you 

 account for the tissue distortions? Can you find the tumor 

 strand in fruit trees? Can you cultivate the parasite from the 

 tumor-strand? From the secondary tumors? 



What causes the browning of the cut surface of the tumors? 



Describe the appearance of the tumors. What effect, if any, 

 do they have on the rest of the plant. Grow sugar beets or 



^ CL 





Fig. 350. — Y-shaped bodies of Bacterium tumefaciens from a young, pure 

 culture treated with acetic acid. Colony 2, resistant daisy, 4 days on agar, then 

 exposed 2 days to 10 drops of acetic acid water (1 cc. acid, 9 cc. water). Smeared 

 and stained with Carbol fuchsin, March, 1915. 



tobacco (I used Nicotiana sylvestris) and inoculate the center 

 of the big rosette of leaves rather early and observe the results. 

 Is there ever stimulating action at a distance from the tumor? 

 Observe in some of the photographs thickening of the wood on 

 the tumor side of the stem. How do you account for it? Ex- 

 amine the plant for stunting, curvatures, changes in color of 

 leaves, death of parts, etc. Does the location of the gall make 

 any difference? 



Histology. — What is the structure of the earliest visible 

 tumors (10 or 15 days from date of needle-pricks) as compared 

 with structure of the tissue inoculated? How do you account 



