FURTHHR Rl-SliARCIIilS IN DlSUASlZS OF PLANTS 373 



collaboration, entitled "A cancerous neoplasm of plants. Auto- 

 nomous bactcria-frce crown-gall tissue." Their summary reads: 



Secondary or metastatic tumors frequently arise on sunflower plants 

 inoculated with Phytoniotuis \_Bacteriurn'] tiitncjacietis at considerable dis- 

 tances trom the primary tumefactions. These have been shown by cultural 

 and serological methods to be characteristically bacteria-free. Tissue cul- 

 tures from these tumors show a rapid disorqanized type of growth con- 

 trasting; sharply with the slow, moderately organized growth of those 

 isolated from healthy tissues. Upon implantation into uninfected plants of 

 the same or related species, these tissues produce typical crown-gall tumors. 

 This capacity for unrestrained, invasive, potentially malignant growth both 

 in vivo and /';; vitro in the absence of the original excitant differentiates 

 these tissues from any other plant materials reported to date and places 

 them in a category comparable to cancerous growths in animals. 



Smith's unvarying aim had been to enlist medical research men 

 to study " the symbiotic action of organisms ... an almost 

 untouched field in medicine and yet . . . one of the commonest 

 and most striking things in Nature, witness the lichen," he said.^'" 

 But he cautioned not to expect as many parasites as there are 

 forms. The ability of experimental scientists to produce " cancer 

 in plants by means of bacteria, in chickens by means of a filter- 

 able virus (Rous), in rats by means of a nematode (Fibiger), in 

 rats by means of a tapeworm (Bullock and Curtis), and in rabbits 

 and mice by means of tar (Yamagiwa, Tsutsui, Fibiger, and many 

 others) " was of utmost significance to him. " The cause of cancer, 

 so far as we now understand it," he urged, ^-° 



may be defined as an irritation acting on an organ or organs unable to 

 withstand it owing to a transmitted or an acquired weakness. Heredity alone 

 cannot cause cancer, but irritation (parasitic and possibly non-parasitic) 

 plus heredity can and does cause it. No such conclusions could possibly 

 have been drawn twenty years ago. They are the measure of the progress 

 we have made. 



In January of 1924, when he sent Dr. Gaylord a reprint, he 

 spoke of this address as " a popular paper " prepared '" with 

 reference to etiology." Smith realized that Dr. Rous and his 

 associates (chiefly Dr. James B. Murphy) had not isolated the 

 " agent or virus " and determined the cause of the chicken sar- 

 comas but, said he, "' experimenting through a series of years 



^^^ Twentietli centuiy advances in cancer researcli, op. cit., 317. 

 ^^"Idem, 316-317. 



