PLINIAN PERIOD 19 



and susceptibility and the explanations offered therefor 

 fall not so far short of present-day progress in this direc- 

 tion. (2) The etiology of disease in plants was largely 

 shrouded in mystery and supersitition. Of the causal 

 relation of living organisms to disease in plants, the most 

 advanced of these ancient thinkers appear to have had 

 not the slightest suspicion. On the other hand, they 

 seem to have had an accurate conception of the causal 

 relation of such factors as drought, freezing, and winds. 

 (3) Their conclusions and recommendation respecting 

 control are odd mixtures of accurate reasoning and blind 

 superstition, as witness the two methods suggested by 

 Pliny for the control of the wheat rust and the smudging 

 urged by Columella for protection of the vine against 

 frost and of the grain against rust. 



