METHODS OF INVESTIGATING PLANT DISEASES. 171" 



METHODS OP INVESTIGATING PLANT DISEASES, 



BY PROF. F. D. HEALD, LINCOLN. 



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That diseases of plants were known and recognized in early 

 times is evidenced by the visitations of "blast" and "mildew" 

 that are mentioned in ancient literature. These maladies were 

 looked upon as due to the displeasure of the dieties, as visita- 

 tions of the Divine wrath, and it was centuries before the human 

 mind sought other explanations. Is it strange that even after 

 centuries of human progress, vague ideas prevail in the minds 

 of some of our less educated people in regard to the true nature 

 of "blights" and "mildews" and various other plant troubles, 

 when we note that as recent as 1846 a scientific investigator 

 attributed our well known "fire-blight" to an epidemic and 

 wrote as follows: "The atmosphere is I believe generally ad- 

 mitted to be the principle by which they prevail, and are carried 

 from place to place. What that subtle principle may be which 

 pervades our atmosphere by which infection is retained and 

 transmitted, so that like the Asiatic cholera it makes the circuit 

 of the whole earth, human science has not discovered. " At a 

 much later date (1897) a noted scientiest affirmed that bacteria 

 do not enter the closed living cells of plants. 



As a boy on the farm I rarely heard of such a thing as diseases 

 of plants, or spraying, or remedial measures of any sort. Such 

 things were not common knowledge as at present. That disease- 

 is as universal in plants as in animals is now generally recog- 

 nized. The last twenty-five years has been a time of rapid 

 progress in our understanding as to the real nature of diseases 

 in plants, indeed I may say that its advances have been greater 

 than in all of the preceding centuries. To-day plant pathology 

 or the study of plant diseases constitutes an important branch 

 of the subject of botany and a field for profitable research for 

 scientific investigators in Universities, Government Bureaus, 

 and Experiment Stations. It may be said with a truth that 

 the time is at hand when ' 'a farmer or a gardener will as little 

 dare to neglect the study of the physiology and pathology of 

 plants as the surgeon will dare to practice without a knowledge 



