Inewton] wheat stem RUST 199 



Miss Allen (1) has recently reported an investigation bearing on 

 this point. She worked with a form of stem rust at Berkeley which 

 produced heavy infection on some wheat varieties, but which on 

 Kanred failed even to produce flecks. She found that although the 

 urediniospores germinated readily on these Kanred leaves, and the 

 germ tubes made their way directly to the stomata, relatively few 

 appressoria entered the stomatal slit. On measurement she found the 

 stomatal aperture in Kanred to be extremely long and narrow, and 

 that of Mindum, a less resistant variety, to have an average width 

 about twice that found in Kanred. This work brings up again the 

 theory which Marshall Ward and his students appeared to have 

 conclusively disproved, viz., that resistance may depend on anatomical 

 adaptations. Our own preliminary investigations, reported in the 

 following pages, tend, however, to support the conclusions of Ward. 



Histological Material and Methods 



Two wheat varieties were used for the experiment, Marquis, a 

 wheat very susceptible to Form XVII, and Kanred, a wheat very 

 resistant to the same form. Seedlings of these two varieties were 

 inoculated in the manner described by Stakman and Piemeisel (59). 

 Portions of the inoculated leaves were removed and fixed daily until 

 uredinia made their appearance on Marquis. As a rule, this took 

 place about the eighth day. Kanred seldom showed any signs of 

 having been inoculated. 



In this way the life history of the fungus was studied from the 

 period of germination up to the formation of spores in Marquis, and 

 until death of the fungus in Kanred. 



For fixing chromo-acetic acid and Flemming's weaker solution 

 were used. On the whole, the best results were obtained with the 

 former solution, in concentrations varying from one per cent, to 

 one-tenth per cent, solution. 



The leaves were embedded in paraffine in the usual manner and 

 the sections cut from 5 to 10 u thick. 



The chief stains used were : 



1. Safranin and light green. 



2. Flemming's orange method (safranin, gentian violet and 

 orange G). 



3. Iron alum haematoxylin, counterstained with safranin, eosin 

 or orange G) . 



