THE CROWN gall: HISTOLOGY 463 



for the small size of the cells? (Young actively growing tobacco 

 stems or daisy stems may be used for this purpose, making 

 shallow pricks.) How many centimeters from the primary 

 tumor to the remotest secondary tumor (using daisy) ? On the 

 sunflow^er shown on Fig. 319, sub. 4, it was 7 inches and on 

 another it was 8 inches (time 5 to 6 weeks) but, of course, mean- 

 while, there was stretching of the stem. Can you demonstrate 

 the tumor-strand? Can you demonstrate the pseudo-stem 

 structure in any of the secondary tumors occurring in leaves of 

 the daisy, the primary tumor being on the stem? Is there any 

 real difference between the structure of the secondary tumors in 

 leaves and those produced on leaves by direct inoculation? 

 Peklo states that he obtained root structure (secondary thicken- 

 ings) in tumors on flower stalks of the sugar beet by direct in- 

 oculation. Is the browned surface of the tumor composed of 

 cork? What is the character of the vascularization of the 

 tumor? Compare the number and direction of the vascular 

 bundles with those of the normal stem and leaf in daisy — in the 

 torus of the sunflower. How do you account for the distortions? 

 For the difference in number of vessels in the two tissues? 

 Does the tumor contain spiral vessels as well as tracheids? Are 

 these abundant or rare? Normal to it or accidental? In cu- 

 cumber leaves which contain spiral vessels and no tracheids I 

 obtained crown galls containing tracheids and free from spirals. 

 Are cambium and phloem normal constituents of the tumor? 

 Can you demonstrate sieve tubes in it? Can you produce 

 tumors without wounding the cambium, Are they vascularized? 

 In such tumors (Fig. 329) how do you account for the tracheids ? 

 Are sieve tubes also present? Is there any tendency in these 

 tumors toward the production of primitive and undifferentiated 

 tissues — structures that occur in early stages of growth, or in 



Fig. 352. — Surface and buried colonies of Bacterium, tumefaciens (hop strain) 

 from Flask P) on +15 beef-peptone agar at end of 4 days at 25°C. Two buried 

 colonies coming to the surface. The surface colonies are smooth and translucent 

 glistening. Photographed January 13, 1917. X14. In agar-poured plates made 

 from old stock cultures the surface colonies of the hop strain are sometimes very 

 unlike those shown on this plate, i.e., they may have a contoured surface and 

 a sinuate margin with a radiate mottled internal structure, yet are infectious. 



