RESEARCH ON Plant Tumors 507 



next dav he read " Meduinism oi tumor t;m\vth in crown ^all," 

 and wrote again: " It seems to mc tremendously important that 

 you can bv opposing the action of the growth inhibitor thru 

 ammonia and various diverse organic acids encourage cell pro- 

 liferation and produce curious races." Geneticist F.. M. East of 

 the Bussey Institution for Research in Applied Biology wrote 

 Smith the following year after reading his paper, " Tmbryomas 

 in plants," and congratulated him on " getting results of the 

 greatest interest and importance." 



The month April 1917 was distinguished by two addresses given 

 by Smith before important gatherings of scientists, and at each 

 he spoke on the subject on which he was now an authority. On 

 April 13, reading a paper before the American Philosophical 

 Society on " Mechanism of Overgrowth in Plants," '•' he reiterated 

 his view that 



the growth in crown gall [is] due primarily to a physical cause, viz., to an 

 increase in the osmotic pressure due to the heaping up locally of various 

 soluble substances excreted by the bacteria as a result of their meta- 

 bolism. . . . The reason I have for thinking the phenomenon of plant 

 overgrowth is primarily physical is the fact that it can be obtained by a 

 great variety of substances not the products of parasites, anything in fact, 

 which disturbs tissue equilibriums without destroying cells, seems to be 

 capable of causing overgrowths, which cease, of course, as soon as the 

 stimulus is exhausted. . . . The first crown galls I studied seemed to me 

 to be overgrowths of the conjunctive tissues and most of our many inocu- 

 lations up^to the end of 1915 produced that type of tumor which corre- 

 sponds, I believe, to overgrowths of the connective tissue of animals and 

 which I have called plant sarcomas. We had found indeed, as early as 

 1908-9, and had produced by bacterial inoculation, plant tumors bearing 

 roots, but the full meaning of this discovery, as related to cancer, did not 

 occur to me until early in 1916, when I found crown-gall tumors bearing 

 leafy shoots on some of our inoculated hothouse geraniums. Beginning 

 with this discovery I made numerous inoculations in the leaf axils of 

 various plants which resulted in the production of leafy tumors, and sub- 

 sequently 1 produced them freely on leaves and on cut internodes where 

 no buds occur normally. Tumors bearing roots have also been produced 

 by us on the top of plants, and in one cut internode of tobacco I succeeded 

 in producing a tumor which bore flower buds. Thcsg perishable root- 

 bearing and shoot-bearing tumors I regard as plant embryomas and have 

 so described them."' 



'''' Proc. Amer. Philos. Soc. 56: A^l-UA, 1917. 

 ''* Idem, quotations at pp. 441-442, 442-443. 



