510 Second European Journey 



the laboratory building and plant houses of the Brooklyn Botanic 

 Garden. The topic of his address was " The Relations of Crown- 

 Gall to Other Overgrowths in Plants." ^° " My own belief," 

 he said, " is that all overgrowths are correlated phenomena, are 

 the response of the organism to essentially similar (but not neces- 

 sarily identical) stimuli, the visible difference in response when 

 brought about by parasites being due to number and location of 

 the parasites, age and kind of tissues invaded, and volume, direc- 

 tion, and velocity of the stimulus exerted." He admitted that 

 " our work on crown gall has opened up more problems than it 

 has settled," but out of it all would come " an eventual better 

 understanding of the whole mechanism of overgrowth." He told 

 of recently producing " galls with diluted crown-gall products," 

 a procedure which suggested " a new method of attacking gall 

 problems in general, especially those in which the gall parasites 

 can be cultivated pure in sufficient quantity for chemical analysis, 

 e. g., various fungi. . . ." 



This technique, he believed, might be extended to the study of 

 plant disorders other than galls. He suggested that 



the application of chemical substances in various dilutions to growing 

 plants or plant organs, such substances in particular as are known or 

 suspected to be produced by living organisms, or are present in soils as a 

 result of decomposition, may prove to be a hopeful way of attacking 

 certain unsolved and difficult problems in plant pathology, e. g., the 

 aetiology of the mosaic diseases, the cause of various growth limitations, 

 etc. 



In his address before the American Philosophical Society, he 

 urged research " on the origin, through absorbed poisons, of 

 certain plant diseases whose etiology [was] very obscure, such as 

 peach yellows, peach rosette, and the various mosaic diseases." 

 His discoveries in crown gall, he believed, might have " interesting 

 bearings " on still other points of research: on the origin of insect, 

 nematode and fungous galls; on the formation of thyloses in 

 vessels; on the origin, through absorbed poisons, of various plant 

 and animal monstrosities; on various problems of modification 

 by slight changes in environment; on the possibility of normal 

 wide distribution of dormant germ-cells among somatic cells; and 

 on the etiology of various human and animal tumors. ^^ 



"Brooklyn Botanic Garden Memoirs 1:448-453, 1918. 

 ^ Mechanism of overgrowth in plants, op. cit., AAl. 



