388 



PLANT GROWTH SUBSTANCES 



healthy artichoke tissue by Camus and Gautheret (9) using the same 

 technique. The possibility that crown gall is actually a virus disease 

 transmitted by a bacterium was discussed by White and Braun (45), 

 and the results of these grafting experiments lend some support to the 

 hypothesis though they do not prove it. 



It remains necessary to say a few words about the experimental 

 inhibition of the growth of vegetable tumors. One of the most important 

 lines of cancer research consists of a quest for a chemotherapeutic agent 

 which will differentially inhibit the growth of cancer cells. This pre- 

 supposes that there is some fundamental difference in metabolism be- 

 tween the cancer cell and the normal. In crown-gall tumor tissue we 

 definitely know that such a difference exists. Crown-gall tumor tissue 

 grows on a medium without added auxin probably because it has acquired 

 the capacity to manufacture its own. It either has more efficient en- 

 zymatic equipment than normal tissue possesses, or it has less exacting 

 requirements and can thus make do with a simpler set of primary 

 nutrients. 



In the course of the past year the writer has studied the effect of many 

 substances on the growth of crown-gall tumors on carrot. These sub- 

 stances included so-called anti-auxins such as 2,4-dichloranisole, anti- 

 biotic substances, sulfonamides, purine and pyrimidine derivatives, and 

 analogues of some of the B vitamins. To test these substances standard 

 fragments of carrot cambial tissue were first inoculated with crown-gall 

 bacteria and four days later, when the tumors were just becoming visible, 

 were treated with 0.05 cc. of a solution containing i part per 1,000 

 of the substance to be tested. The fragments were incubated for two 

 weeks then examined for tumors. 



The anti-auxins, antibiotic substances, and sulfanamides used were 

 found unable to inhibit tumor growth once the tumor had been initiated. 

 Streptomycin was capable of inhibiting tumor formation but this seemed 

 due to its action on the bacteria rather than on the tumor tissue. Com- 

 plete inhibition of tumor growth was obtained with certain analogues 

 of folic acid. These compounds had already been tested on animal cancers 

 and found to have an inhibiting effect on the growth of tumor tissue, 

 though their high toxicity limited their therapeutic value. The sub- 

 stances found most active in inhibiting the growth of crown-gall tumor 

 tissue on carrot are issued by Lederle Laboratories under the names 

 Aminopterin, A-methopterin, A-denopterin, A-ninopterin and A-terop- 



