1915] 



SMITH BACTERIAL DISEASES OP PLANTS 



391 



bacterium following hard after and often doing the major part 

 of the damage. The reverse of this also occurs, the bacterium 

 entering first and the fungus following. ! 



Parasitic bacteria are soon followed by saprophytic bacteria 

 which complete the destruction of the tissues, and, if the dis- 

 ease is somewhat advanced, cultures from the tissues may 



yield only the 



(potato rots). Also, as in animals 



parasitic disease may follow another and the second be more 

 destructive than the first, e. g., fire-blight following crown-trail 

 on the apple. 



EXTRA-VEGETAL HABITAT OF THE PARASITES 



Here is perhaps the place to say a few words about the non- 

 parasitic life of the attacking organisms. 



All are able to grow saprophytically, i. e., on culture media 

 of one sort or another, and probably all live or may live for 



soil. Very few, however, have been cultivated 



time in the 



from 



The vast mixture of organisms present in a good 



earth rather discoura 



6 



In some of the unsuccessful 



attempts failure may have been due to not having undertaken 



at exactly the right time, or in just the right 

 the proper medium, but more often probably 



swamping tendency of rapidly growing saprophytes, 

 long a parasite is able to maintain its virulent life in a 

 must depend largely on the kind of competitors it finds, 

 have used the term virulent, because it is conceivable that 

 organism might remain alive in a soil long after losing 



How 



I 



infect plants, just as we know it can in culture media 



ium Solana 



o 



brown rot of Solanaceae 



Bacillus phytophthorus causing basal stem rot and tuber 

 of the potato, and Bacterium tumefaciens causing crown-; 



such soils, especially 

 disease, if thev belon 



)il, and the soundest plants when set in 

 if wounded, are liable to contract the 

 to susceptible species. The root-nodule 



organism of Leguminosae, which I have not considered here 

 also lives in many soils, as every one knows. 



