216 



BACTERIAL DISEASES OF PLANTS 



' JF 



* 



have time and a place include a variety test in your inoculations. 

 Determine if the shoots of the potato are susceptible (do not 

 expect rapid infection) ; look for it in the field upon potatoes : 

 (a) stems; (b) tubers. (Read Spieckermann's papers.) 



Transmission. Determine whether I am right in thinking 

 that the organism freely oozes to the surface of diseased tomato 



plants, and that infections are 

 ' t * | commonly above ground 



^ through stomata. 



' *". ^ % It is very important to 



* - know whether it is borne on 



v , tomato seeds (I believe it is, 



/ - since it resists drying and we 



find it very commonly in the 



~ -, * / fruits). If so, it may come 



* ~ - > into the field from the seed 



bed, as in case of Bacterium 

 campeslre (No. II). To estab- 

 lish this conclusively, I have 

 done it only inferentially, 

 would be a fine practical con- 

 tribution to our knowledge of 

 the disease. 



Once in the field, how is 

 the organism carried from 

 plant to plant? Rains ex- 

 cluded, it can scarcely be wind- 

 borne, do you think? If you 

 have opportunity to study this 

 disease in the field (the writer 

 has not had) you should ex- 

 amine particularly for carriers of infection (insects, etc.), for 

 evidence of under-ground infection, i.e., through the root-system, 

 and for transmission on seeds taken from diseased plants. The 

 disease was so prevalent and destructive at Grand Rapids, 

 Michigan, that seemingly it must have begun early in the life 

 of the plants. 



It escaped from my control in one of the Department of 



I 



FIG. 159. Rods of Aplanobacter 

 michiganense. From an agar culture 2 

 days old, stained by van Ermengem's 

 silver nitrate method. X 1000. 



