REMEDIAL MEASURES. 167 



have been driven. True, we cannot always trace 

 the tangled skein of inter-relationships between 

 one organism and another in Nature : the recog- 

 nition of the principle of natural selection and the 

 struggle for existence is too recent, and our 

 studies of natural history as yet too imperfect to 

 lay all the factors clear, but no observant and 

 thoughtful man can avoid the truth of the general 

 principle here laid down. The history of all 

 great planting enterprises teaches us that he who 

 undertakes to cultivate any plant continuously 

 in open culture over large areas must run the 

 risk of epidemics. 



Notes to Chapter XVII. 



The principal literature, now very voluminous, on this 

 subject is contained in the publications of the U.S. Depart- 

 ment of Agriculture from 1890 onwards. See especially 

 Bulletins, Nos. 3, 6, and 9 ; Farmers' Bulletin, No. 91, 1899 ; 

 and The Journal of Mycology during the same period. See 

 also Lodeman, T/ie Spraying of Plants, London, 1896. A 

 summary of the principal processes will be found in Massee, 

 Text-Book of Plant Diseases, pp. 31-47. 



With regard to the history of the subject, which still needs 

 writing, the reader should not overlook Roberts, " On the 

 Therapeutical Action of Sulphur," St. George's Hospital 

 Reports, date unknown, but subsequent to the following : 

 Berkeley, Introduction to Cryptogaviic Botany, 1857, p. 277, 

 with references. These are, I believe, with the references to 

 steeping of wheat in De Bary, Unters. iiber d. Brandpilze, 

 Berlin, 1853, among the first attempts to utilise such remedies. 



Further facts will be found in the pages of the Gardefiers' 

 Chronicle, especially since 1890, and in Zeitsch.f. Pflanzen- 

 krankheiten since 1891. 



