438 BACTERIAL DISEASES OF PLANTS 



some hours to diffuse. Then make the plates, pouring some 

 directly from the tube containing the mashings and others 

 from dilutions of it (several drops of the cloudy fluid into the 

 second tube of bouillon, and after it has stood for an hour, with 

 some shaking, 1 2 cc. from this tube into a third tube of bouillon). 

 Rarely does one obtain colonies on plates poured from the 

 dilutions when first made. Moreover, if your material is scanty 

 you will of course save not only the remains of the tumor but 

 also your original tube and the dilutions made therefrom, and 

 pour another series of plates next day, but if there is a green 

 stain or if gas is forming in the tube containing the mashings, 

 then pour only from the dilutions. For these poured plates 

 use +15 peptone-beef agar. 



On the poured plates all yellowish, orange, greenish, or 

 pinkish colonies, all branching white colonies, and all circular 

 white colonies, if opaque, are negligible. Only those colonies 

 that come up slowly, that remain for a considerable time small, 

 circular, raised and glistening-translucent (watery) need be 

 considered (Figs. 351, 352). Even following this advice some 

 of the colonies selected for the sub-cultures (which may be on 

 agar or potato or in bouillon) may not prove to be infectious, 

 therefore it is advised to experiment with quite a number of 

 colonies, and to examine them by transmitted light, rejecting 

 all that show a narrow clear zone about the colonies even if 

 they look right by reflected light. 



For inoculation purposes the student has choice of many 

 kinds of plants since many are susceptible. For class work the 

 young and rapidly growing roots of turnips or sugar-beets, the 

 soft shoots of tomatoes. Pelargoniums, castor oil plants, or 

 Paris daisies, and the crowns of young peach, almond, or poplar 

 are recommended. Shoots and crowns of the hop or the 

 European grape, if growing satisfactorily, may also be used; 



July 7, 1916, on the cut surface of the middle of an internode of the main axis 

 near the top of the plant just before blossoming time, by needle pricks, using a 

 pure culture of the hop strain of Bacterium tumefaciens, which had been passed 

 through sunflower. Photographed August 4, 1916. Natural size. There were 

 1 1 flower-})uds on this date but a day or two later they began to fall off without 

 opening. The big side branches developed after the inoculation. 



