516 MICROBIAL DISEASES OF PLANTS. 



CAUSAL ORGANISM. Erwin F. Smith describes Bacillus tracheiphilus as a rod 1.2^ 

 to 2.5^ by o. 5/i to 0.7 /t, actively motile when young. 



Growth occurs on the ordinary media. Upon agar, the growth is milk-white and 

 extremely viscid. Upon potato, a gray film is produced, much like that of B. typhosus; 

 the potato is unchanged. Gelatin is liquefied and no change occurs in milk. Acid 

 but no gas is produced in saccharose and dextrose broths. The organism is aerobic and 

 possibly facultatively anaerobic. Optimum temperature is between 20 and 30. No 

 growth at 37. Thermal death-point, 43. 



CONTROL. The same precautions and preventative measures are to 

 be recommended for the wilt of cucurbits as are given for tomato blight. 



LEAF DISEASE or NASTURTIUM.* 



A wilted, discolored condition of nasturtium leaves has been shown 

 to be due to a microorganism of the genus Bacterium, described but 

 not named. 



WILT OF SWEET CORN. 

 Pseudomonas stewarti Smith. 



The early varieties of sweet corn grown in the truck gardens of Long 

 Islandf are subject to a bacterial disease which manifests itself by a wilting 

 and drying up of the leaves. It also occurs in Iowa, and it has been re- 

 ported from certain parts of New Jersey. 



The wilting may occur at any stage of growth, but the plants seem to be 

 more susceptible at the time of flowering. As a rule the leaves succumb 

 one at a time, although on the younger plants they may all wilt simultane- 

 ously. There is no external evidence which would indicate the cause of 

 the trouble, but if a diseased stalk is cut lengthwise, the nbro-vascular 

 bundles appear as yellow strands in the white pith. A crosssection of such 

 a stalk will show drops of a yellow viscid substance, composed largely of 

 bacteria, exuding from the cut ends of the bundles. The infection is not 

 confined to the stalks but can be found in the vascular system of the leaves, 

 husks and cobs as well. The vessels are the principal structures invaded, 

 but in time small cavities filled with the bright yellow slime are formed 

 in the surrounding parenchyma. 



METHOD OF INFECTION. The germ may enter its host through either 

 the roots, stomata or water pores and when once inside the vascular 



* Jamieson, Clara O., Science, N. S., Vol. XXIX, 753, p. 915, 1909. 

 f Stewart, F. C., " A Bacterial Disease of Sweet Corn," Bull. 130, N. Y. Agr. Exp. Sta. 1897. 



