VARIETAL RESISTANCE 283 



other hand, it is possible that it may depend upon characters 

 associated with growth and which vary with the age of the plant. 

 Such characters might comprise silica content, hardness or thick- 

 ness of cuticle, hairiness, sap qualities, etc. Since it has been 

 shown (p. 264) that susceptibility appears to be correlated with 

 the age of the plant, one or more of these features may be involved. 



In Cunliffe and Fryer's experiments twelve varieties of oats 

 were grown in two widely separated localities, viz., Sandford 

 (Oxon.) and Harpenden (Herts). The infestations of both stem 

 and panicles were noted in detail, and the results obtained were 

 subjected to statistical analysis. The correlation between stem 

 infestation of different varieties at the two localities was high, 

 but the grain infestation exhibited no correlation whatever. Of 

 the varieties submitted to experiment, Goldfinder and Supreme 

 are those least and most subject to infestation, respectively. 

 Consistent and significant differences in the extent of shoot 

 infestation, of the order of 20 per cent., were noted in favour of 

 Goldfinder. Unfortunately, correlated decrease of seed infestation 

 was not so marked ; Goldfinder was not in the group suffering 

 least infestation, but it suffered less than 5 per cent, heavier 

 attack than those varieties least attacked. The variety New 

 Abundance was found to be almost equal to Goldfinder in its 

 freedom from the stem infestation, but, on the other hand, it was 

 decidedly the heaviest sufferer from the grain attack. 



It is not possible to say how far the results of these experiments 

 can be held to be of general application. The fact, however, that 

 such varietal differences do exist is hopeful for the future. The 

 great difficulty in many parts of England is to sow oats sufficiently 

 early to escape attack, owing to the fact that weather and soil 

 conditions are frequently adverse to this procedure. It seems, 

 therefore, that the chief hope for the future lies in the production 

 of varieties which combine resistance with good yield, since 

 heavy yielding strains for the most part occupy inferior positions 

 in the scale of resistance. Cunliffe (1936) describes a series of 

 experiments designed to ascertain whether it is possible to breed 

 resistance to attack by this insect into the best varieties of English 

 oats, which are highly susceptible. It appears that the most 



