466 BACTERIAL DISEASES OF PLANTS 



related plants? See Figs. 353, 354, 415, 416, 417, 418, and 

 Bulletin. 255, PL LVI (for the wide medullary ray) for what I 

 mean. Toward the production of giant cells? What is a 

 giant cell? How does the structure of the teratoid crown gall 

 differ from that of the non-teratoid gall? On tobacco internodes 

 the writer obtained tumors bearing leafy shoots not only from 

 the cambium but also from the protoxylem and from the bark. 

 How do crown galls differ in structure from fungus galls? 

 From insect galls? From nematode galls? How do you ac- 

 count for these differences? For structure of the tumor and 

 tumor-strand, cut cross-sections, and longitudinal sections 

 of leaves and stems (between tumors and through them) from 

 fixed material embedded in paraffin. Stain 6 to 24 hours in a 

 2 per cent aqueous solution of methyl green, and after rinsing 

 in water gently so as not to w r ash off the sections, counter- 

 stain 5 to 15 minutes in a 2 per cent aqueous solution of acid 

 fuchsin (not basic fuchsin). Then pass very rapidly through 

 graded alcohols into absolute alcohol, xylol and Canada bal- 

 sam. The right amount of staining should be judged under 

 the microscope as it is proceeding. Do not overwash the 

 sections. 



Such sections may also be stained in various basic aniline 

 dyes to demonstrate absence of the bacteria in the vessels and 

 intercellular spaces, but the student will hardly be able to dem- 

 onstrate the bacteria in the tissues, i.e., inside the cells, by means 

 of aniline dyes, unless he should have better success than the 

 writer and his assistants have had. They may be demon- 

 strated by allowing them to diffuse out of the cut tissues in 

 bacteria-free water on slides free from bacteria, i.e., clean 

 flamed slides, which should then be dried and stained with 

 Ziehl's carbol fuchsin, which should also be free from bacteria. 

 Both rods and Y's can be demonstrated in this way. They 

 should be studied under the 2-mm. oil immersion objective, 

 using a No. 8 or No. 12 ocular. 



Certain bodies which at one time I identified as bacteria are 

 best demonstrated in the tissues by cutting small slices (2 mm. 

 thick) from young and tender galls and throwing them for 24 

 hours into 5 or 10 cc. volumes of a 5 per cent aqueous solution 



