SMITH: CROWN GALL AND OTHER OVERGROWTHS 453 



IV. Other effects of parasitic excretions. I believe also from what I 

 have seen and have obtained to some extent by experiment 

 that thyloses, fasciations, distortions of tissues, and various 

 duplications, simplifications and inverse tissue differentiations 

 are caused by the excretions of feeble parasites although in 

 nature probably, all are not so caused. 



Finally, I would suggest 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 decompositions, 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. 



Literature 



Those who wish details on crown gall are referred to the following 

 papers : 



For the older work: Science, N. S., April 26, 1907; Phyto- 

 pathology, Vol. I, No. I, Feb., 191 1; Science, N. S., February 2, 1912; 

 i" Congres International de Pathologic Comparee, Tome II, Paris, 

 1912; 17th International Congress of Medicine, London, 1913, Sec- 

 tion III, General Pathology; and Bulletins 213 and 255, Bureau of 

 Plant Industry, to be had from the Superintendent of Documents, 

 Government Printing Office, price 40 and 50 cents, respectively. 



For the newer work so far as published: The Journal of Agri- 

 cultural Research, April 24, 191 6; The Journal of Cancer Research, 

 April, 1916; Science, N. S., June 23, 1916; The Journal of Agricultural 

 Research, January 29, 191 7; Bulletin of the Johns Hopkins Hospital, 

 Sept., 191 7; and Proceedings of the American Philosophical Society, 

 Vol. 56, 1917. 



Separates of most of these papers may be had from the writer. 



