Studii-s on Crown CIaii. oi Plants 455 



isolated and rcisolatcd in pure culture and by means of which wc tan 

 produce the disease at will. 



Again he answered the reply of certain cancer specialists that 

 crown galls are evidently a granuloma and not a true tumor, 

 citing in his discussion tuberculosis and syphilitic gummata as 

 instances of granulomata and differentiating malignant animal and 

 human tumors. In part, the difference was, as he viewed the 

 problem, that in granulomata the parasite migrates whereas in 

 cancers the cancer cell itself migrates, that is, " some of the body 

 cells which under some unknown stimulation have been taken out 

 of the physiological -control of the body and have become thus, 

 as it were, parasites on their fellow cells." In plants there is no 

 rapid bloc:)d stream, such as animals have. How, then, was the 

 tumor strand and its propagation to be explained.^ The strand 

 had been discovered in the inner wood next to the pith between 

 a secondary and a primary tumor and near the primary tumor, 

 and, further, it was found to be not merely local but traceable 

 for some distance and occurring with regularity in the normal 

 tissue bet\veen the primary and secondary tumors. Smith exhibited 

 lantern slides showing cross and longitudinal sections of such 

 strands from inoculated plants. On this strand had been found 

 developed secondary tumors. " In the Paris daisy, when the 

 primary tumor is on the stem," he explained, 



secondary tumors often develop on the leaves, and strands of tumor tissue 

 have been traced in numerous instances all the way from the primary 

 tumors throui^h the stem into the leaf, and all stages of the development 

 of the secondary tumors observed on many plants. This tumor strand 

 boring its way through stems and leaves appears to be as much a foreign 

 body as the roots of a mistletoe or the mycelium of a fungus. From these 

 strands and from these secondary tumors we have isolated the same micro- 

 organism that occurs in the primary tumors and with subcultures from such 

 bacterial colonies have reproduced the disease. The discovery of this strand 

 affords a satisfactory explanation for the fact that the morbid growth 

 usually returns after excision. 



The second striking fact to which I wish to call your attention is that 

 when the primary tumor occurs in the stem and the secondary tumor in 

 the leaf the structure of the secondary tumor is not that of the leaf in 

 which it is growing, but of the stem from which the strand was derived. 



The Bulletin de I'lnstitut Pasteur reviewed this address, and on 

 June 22, 1912, Smith thanked Dr. Weinberg. He promised to send 



