CHAPTliR XI 



FURTHER DISCUSSION OF TI IF CROWN GALL-ANIMAL CANCER 



ANALOGY-VARIOUS ASPECTS OF FACT AND THEORY. A SUGGESTED 



MULTIPLE FACTOR HYPOTHESIS OF PATHOLOGICAL GROWTH. 



FURTHER RESEARCHES IN BACTERIAL, FUNGOUS, AND 



VIRUS DISEASES OF PLANTS 



BY 1920 Smith had published more than twenty-five papers, 

 aside from his books, on crown gall. His laboratory was 

 becoming recognized as doing probably more research on bac- 

 terial diseases of plants than any other laboratory in the world. 

 He realized that he was breaking " new ground for the benefit 

 of other workers," and in his text. Introduction to Bacterial Dis- 

 eases of Plants,'^ more than writing on methods of research, 

 fourteen selected diseases including crown gall, and a general 

 conspectus of the subject, he suggested fifty-one subjects for 

 special study and supplied notes on thirty-four additional maladies. 

 Mention of a few of his topics for future research gives some 

 idea of their scope: natural and acquired immunity and resistance 

 to disease in plants and the effect of hybridization; symbiosis and 

 antagonism among the lower plant organisms and the possibility 

 of solving diseases by discovery of new methods; causes of mosaic 

 and virus diseases, tobacco mosaic, peach yellows and rosette, 

 pecan rosette, etc.; new adaptative and differential culture media; 

 critical study of the chemistry of tumor-producing species from 

 variously aged flask-cultures in various media; the determination 

 of all acids produced by plant pathogens, and the hydrogen-ion 

 content of media as related to growth of plant pathogenic species; 

 the continued study of plant nutritive components, soil and climate 

 relations, in plant diseases; insect and other animal distributors of 

 diseases and their control; and many other problems. 



Since 1917, especially since his treatise, " Mechanism of Tumor 

 Growth in Crowngall," scientific interest in the crown gall-animal 



^ W. B. Saunders Co., Phila. and London, 1920. At pp. 474-477 appeared his 

 " suggestion of subjects for special study " ; at p. 473, " notes on some additional 

 diseases." At this time, furthermore. Smith offered to research pathologists study 

 materials. 



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