STEWARTS DISEASE OF MAIZE: CAUSE 



163 



first plunge the seeds momentarily into alcohol, rinse them 

 very lightly and dry quickly or plant at once. Why this last 

 direction? Why also first into alcohol? It fills the infected 

 vascular bundles with a yellow slime which oozes on cross- 

 section (unless the plants have been frosted). Why not then? 



Fig. 102. — ^Cross-section of a diseased sweet-corn stalk showing A-planohader 

 stewarti oozing from the bundles. Planar enlargement. 



Technic. — Isolations may be made from externally sound 

 upper internodes of the maize stem, by the first method de- 

 scribed under No. I. Often pure cultures may be obtained 

 directly from the cut stem by streaks on steamed potato or 



Fig. 103. — Water mount of a sweet-corn stem in longitudinal section showing 

 Aplanobacter stewarti oozing from a vascular bundle like smoke from a chimney. 

 {After F. C. Stewart.) 



nutrient agar if the surface sterilization has been thorough, 

 but if so made, subsequently they should be plated out. It 

 is more difficult to isolate from the interior of kernels. Such 

 kernels should be soaked in 1 : 1000 mercuric chlorid water 

 for 30 to 60 seconds, to inhibit, rather than to kill, surface 



