438 SMITH—MECHANISM OF OVERGROWTH IN PLANTS. 



which stimidus, it is very hkely, is not only very minute in quantity 

 but also used up during the growth of the tumor cells, that is, 

 converted into something quite different and entirely inoft'ensive. 

 For this reason analyses of tumor tissue should give only about the 

 same kind and quantity of products as normal tissues in which 

 there is an equally rapid movement of food-stuffs, and in which 

 there is an equally rapid growth, and this is about what tumor 

 analyses thus far have shown. In flask cultures, on the contrary, 

 the products of parasitic growth accumulate and can be locked up 

 for future study. 



What I have done, in addition to speculating, is to grow 

 various strains of Bactcr-iuui tmucfacicns, the crown-gall organism, 

 in pure culture in quantity in cotton-plugged Jena glass flasks for 

 chemical examination. Being a member of the United States De- 

 partment of Agriculture, the greatest cooperative research institu- 

 tion in the world, it has been easy to come into touch with expert 

 organic chemists and through them to have determined for me the 

 various substances produced by the crown-gall organism out of 

 river water, peptone and grape sugar, i. c, substances correspond- 

 ing to or approximating those which occur naturally in the cells 

 of the plant. These flasks were inoculated with great care and 

 watched as to their behavior. Before turning them over to the 

 chemist, Petri-dish agar plates were poured from each one to de- 

 termine whether they were still pure cultures. The analyses were 

 then made pari passu with inoculations into susceptible plants to 

 determine whether the cultures were still pathogenic. In this way 

 various flasks were tested and worked up separately, with, in the 

 main, concordant results. The inoculated flasks behaved properly, 

 the agar-poured plates yielded uniform normal-looking colonies, and 

 subcultures from colonies derived from each flask were subsequently 

 inoculated into plants with the production of crown galls in every 

 case except that of the isolation from poplar, which was known to 

 be no longer pathogenic when the experiment was begun. All of 

 the flasks had remained pure cultures and were in good condition 

 for the chemist, who worked them over quickly. These cultures 

 originated from single colonies selected from agar-poured plates 

 made from tumors on hop, Paris daisy, rose and poplar, and repre- 

 sent at least two strains of the crown-gall organism. 



