12 



MASS. EXPERIMENT STATION BULLETIN 400 



development and distribution to the trade. For three consecutive years a number 

 of these commercial rust-resistant varieties were tested at Waltham for reaction 

 to rust under field conditions. 



Results of these observations are shown in Table 5. Most of the varieties 

 showed a rather high degree of resistance to rust, but a few had a rather low degree 

 of resistance. The degree of susceptibility to rust varied from j'ear to year, which 

 may be explained in part by the difference in hereditary constitution of the 

 varieties themselves, and in part by variable climatic conditions that may have 

 affected the development or distribution of the rust through the plantings. In 

 several instances where held-over seed of certain varieties was available for plant- 

 ing the following two years for comparison with current seed stock, reaction to 

 rust apparently was influenced in some way by climatic conditions. Plant vigor 

 in almost all the varieties was good, but considerable variation in the type of 

 foliage was noted with the individual varieties. The following varieties were 

 acceptable garden types under conditions at Waltham: Alaska, Fair Lady, 

 Buttercup, Salmon Pink,, Daffodil, Maximum White, Yellow, and Crimson. 



Table 5. Rust Reaction on Introduced Resistant Garden Varieties 

 OF Snapdragon Tested at Waltham. 



Variety 



Percent of 

 Plants Resistant 



1937 1938 1939 



\"ariety 



Percent of 

 Plants Resistant 



1937 1938 1939 



Alaska 83 98 87 



1937 Seed 66 93 66 



Buttercup 97 93 



Canary Bird 92 



California (Uni\'ersit\) 



Mi.xture 66 97 52 



1935 Seed 97 



1937 Seed 91 



Campfire 89 97 98 



Daffodil 78 97 79 



Defiance 79 98 



1937 Seed 97 



Fair Lady 84 95 



1937 Seed 97 



Golden Orange 87 98 97 



1937 Seed 98 



Indian Girl 67 97 



1937 Seed 97 



Orange Pink 98 98 



Opal Queen 96 



Pinkie 



Rose Sensation 



Salmon Pink 97 95 



1937 Seed 95 



Silver Pink 89 79 



Swing Time 



Maximum White .... 95 98 

 1937 Seed 97 



Maximum Yellow .... 97 98 



Maximum Crimson 



Wild Fire 98 98 



98 

 79 



78 



40 

 90 



77 

 97 



The Susceptibility of Other Species of Antirrhinum to Rust 



Where a fungus disease becomes of economic importance to crop production, 

 the inquiry as to plant resistance may be directed to individual crop plants or 

 to related genera and species. Blasdale (1) has reported the susceptibility of 



