PAPERS ON BIOLOGY AND AGRICULTURE 143 



ecological character, of important conclusions of an epi- 

 demiological nature, and may even lead to the possibility 

 of predicting with reasonable certainty whether or not 

 epiphytotics of any disease should be expected in a given 

 season. 



It is probable that some distinction exists between what 

 should be considered as "survey" and what "inspec- 

 tion". The work of a survey may be said to be of a more 

 extensive nature, concerned with the whole aspect of a 

 problem, rather than with anj' small part. For the pres- 

 ent at least the Plant Disease Survey finds it impossible 

 to consider j)lant diseases in any greater detail than as 

 to how they affect whole counties. Counties are chosen 

 as an arbitrary unit for lack of any sufficient ecological 

 or agricultural stratification of the state. 



DETEEMINIXG DAMAGE DOXE 



This is probably the most difficult phase of the work 

 which the Plant Disease Survey plans to undertake. 

 Under any circumstances, estimates of damage are bound 

 to be merely relative. In the case of grains, for example, 

 while one may determine rather accurately the damage 

 done to a given plant by such diseases as smut and scab 

 where it is considered that the loss is limited largely to 

 the affected grain, these diseases which are of a more gen- 

 eral!}' parasitic nature such as the rusts present problems 

 in estimation that are difficult in the extreme. Arbitrary 

 scales for judging the percentage of infection on a given 

 plant might serve admirably for this purpose were it not 

 for the numerous complicating factors. In the case of 

 rust, where the ultimate damage is apparent mostly in the 

 shrivelled grains, there are other factors tending toward 

 the weakening of the plant and the smallness of grains, 

 such as early ripening in dr^^ and hot weather, the pres-' 

 ence of minor parasitic agents such as Helminthosporium, 

 glume blight, etc. 



It is, nevertheless, very necessary that some sort of 

 estimate of damage be made because it will have a very 

 real value in pointing out, if only in a relative way, the 

 true importance of plant diseases in limiting crop pro- 

 duction, and in indicating where there is need either of 



