STEWARTS DISEASE OF MAIZE I HISTOLOGY 



171 



present in the leaves themselves? Are such large leaves ever 

 infected first at the apex? Make cross-sections: a at the tip; 

 6 near their junction with the 

 stem ; and c in the middle of the 

 leaf. Try several leaves. 

 Have you seen any evidence of 

 wound-infection? If diseased 

 ears are available, study care- 

 fully by means of sections at 

 different levels the upward and 

 outward movement of the bac- 

 teria in the pedicle, cob and 

 husks. Try to demonstrate vas- 

 cular infection in the base of 

 the kernel. 



Observe yellow pockets in 

 the pith and in the husks. 

 Make sections and determine 

 the contents of these yellow 

 spots. Draw what you have 

 seen. 



Have you observed any 

 brown stain in the stems? Is it 

 local or general? Where does 

 it first begin? Is this stain a 

 host reaction? Does the organ- 

 ism cause a brown stain in any 

 cult ure medium ? Compare 

 with No. II and No. X. 



What impresses you most 

 about this disease? Do vou 



j 



think there are any toxins liber- 

 ated? What are your reasons? 

 How many bacteria would you 

 estimate to be present in an in- 

 fected well-grown plant when 

 the leaves are beginning to shrivel? What proportion of the 

 vascular bundles are occupied? Is there anything correspond- 



FIG. 113. Sweet-corn plant de- 

 stroyed by Aplanobacter stewarti as a 

 result of an inoculation on the leaf- 

 tips in the seedling stage. Plant 

 dwarfed and vessels full of the yellow 

 slime. Time, more than 60 day>. 

 District of Columbia, 1902. 



