THE CUCURBIT WILT: HISTOLOGY 141 



Does it ever come to the surface as an ooze on attacked 

 plants. Contrast with pear bUght (No. XII, Figs. 282 to 285). 

 Make permanent sUdes. Stain with Ziehl's carbol fuchsin. Try 

 at least two other stains. 



Variahility. — How long does an attacked plant live? 



Have you seen any indications of immunity on the part of 

 inoculated plants? of recovery? of slow development of the 

 disease? Study this especially in squashes. 



4* * '^^ 



Fig. 72. — Cross-section of a squash petiole from one of my inoculated plants. 

 Every bundle is occupied by the bacteria which are stained. They are also to 

 some extent in the parenchyma around the bundles. From a planar enlargement 

 by the writer. 



What effect, if any, does heavy vs. light watering have 

 upon the progress of the disease? Why are not all susceptible 

 cucurbits destroyed by this organism? 



Transmission. — If time, season, and location permit, at- 

 tempt transmission of the disease by insects. Try Diahrotica 

 vitatta or Diahrotica 12-punctata collected from healthy plants. 

 Starve 24 to 36 hours, feed on freshly wilting leaves for a short 

 time only (early evening), then liberate (over-night, or a less 

 time if they have bitten the plants freely) in insect cages con- 



