I 



90 DISEASE IN PLANTS. 



forth. Consequently the science of plant patho- 

 logy is much concerned with the direct action of 

 external causes, which are probably less obscure 

 than in the case of animals, though by no means 

 always obvious. Such considerations at any rate 

 seem to account for the fact that most authorities 

 on plant pathology base their classification on the 

 causes of disease, there being few noteworthy 

 exceptions. 



Notes to Chapter IX. 



The bibliography here quoted will be found in Berkeley, 

 "Vegetable Pathology," Cardcfier's Chronicle, 1854, p. 4; 

 Plowright, British UrediitecB and Ustilaginea, 1889; Eriksson 

 and Henning, Die Getreideroste, Stockholm, 1896 ; De 

 Bary, Comparative MorpJiology and Biology of the Fungi, 

 etc., 1887 ; Frank, Die Kratikheiten der PJlanzen, 1895-96, 

 and scattered in the works referred to in them and in the 

 text. 



