4 EELATION OF CEOWN-GALL. TO LEGUME INOCULATION. 



clusively that this is not only an infectious disease caused by a spe- 

 cific micro-organism {Bacterium fumefaciens), but that it can infect 

 many kinds of pLants. For instance, the bacteria isolated from the 

 crown galls of peach trees will produce excrescences upon the stems 

 or upon the roots of tomatoes, sugar beets, salsify, rose bushes, apple 

 trees, certain of the legumes, etc. The same is true of bacteria iso- 

 lated from these abnormal galls, or tumors, upon sugar beets, and, in 

 fact, it is probable that the crown-gall bacteria isolated from any one 

 of the kinds of plants showing the disease will produce similar dis- 

 eases in any of the other kinds of plants Avhich have been found 

 infected. 



THE DISTINCTION BETWEEN CROWN-GALL TUMORS AND 

 NITRQGEN-FIXING NODULES. 



Fortunately, the difference between nodules produced by the bene- 

 ficial nodule-forming organism of the legumes and those produced 

 by the crown-gall organism is sufficiently typical to be easily recog- 

 nized by an experienced observer. If it is desired to use soil for 

 inoculating new fields, an examination of the roots of the legume 

 growing upon the old field would readily show Avhether the soil is 

 suitable for distribution. The slight external difference between 

 the crown-gall tumor and the nitrogen-fixing nodule is shown in 

 Plate I, in which figure 1 shows the nitrogen-fixing nodules of alfalfa ; 

 figure 2, the crown-gall tumors ; figure 3, the nitrogen-fixing nodules 

 of crimson clover; figure 4, the crown-gall tumors. Though it may 

 be possible to confuse these during a hasty examination, it is obvious 

 upon close inspection that the nitrogen-fixing nodule is an outgrowth 

 from the plant root, and that it has no more apparent effect upon the 

 root than has an ordinary branch of the root. The interior of the 

 nodule contains flesh-colored cells full of bacteria, which may be 

 easily seen under the microscope. The crown-gall tumor, on the other 

 hand, causes much distortion of the root, frequently forcing it to 

 branch into many small roots, which project from the tumor itself. 

 The interior of the tumor is white and it is difficult, if not impossible, 

 to see any bacteria in any of the cells, even in the most carefully pre- 

 pared sections of the tumor tissue. 



With the facilities of a bacteriological laboratory it is not especially 

 difficult to determine whether cultures distributed for inoculating 

 legumes contain the crown-gall bacteria or the nodule-producing bac- 

 teria. The three tests most useful for a rapid diagnosis are as 

 follows: Pour petri-dish plates with special colored agar.^ The 

 nodule- forming organism does not absorb the color, and grows as 



1 Water, 1,000 cubic centimeters; sugar, 10 grams; potassium phosphate (monobasic), 

 1 gram ; magnesium sulphate, 0.2 gram ; agar, 15 grams ; and congo red, 0.1 gram. 

 [Cir. 76] 



