Cellular Growth 105 



increased to 2 per cent, other poisonous actions occur. Alcohol acts 

 as an antidote with resjxct to c-mitosis and tlie c-tumor. 



When two chemicals work together to accelerate an activity be- 

 yond the effect obtainable by each chemical independently, the re- 

 sponse is known as a synergism. Colchicine and numerous other 

 chemicals have been tried for their synergistic action.'*^ Some give 

 accelerated response and others do not. Phenylurethane along ^vith 

 colchicine increases the action of drug upon roots of Allium.^'^ 



Tissue cultures of HeliunUius tuberosus were handled by com- 

 bined treatments of heteroauxin (lO-o) and colchicine (10 6) . Small 

 doses of colchicine enhance the action of heteroauxin because the 

 tissues seem to divide more actively and huge cells with many chromo- 

 somes develop as a result. A stimulating action seems evident from 

 these experiments. Increasing the concentration of colchicine leads to 

 repetitive c-mitoses and an inhibition of cellular multiplication 

 among the tissues. ^^ 



Generally, favorable conditions for growth increase the promotion 

 of a tumor from a specific treatment.'^^ The range in concentration 

 is fairly broad, but there are limits marked by minimum and maxi- 

 mum concentrations, rhe formation of tumors within certain limits 

 is proportional to concentration. Finally, the thresholds for c-mitosis 

 and c-tumors are close to each other with some indication that the 

 threshold for the latter process is lower than that for c-mitosis.s^ 



As soon as the independence of c-mitosis and c-tumor was sus- 

 pected, a specific experiment was designed to test autonomy.''' Root 

 primordia of AlUinn fistulosum were subjected to intense X-ray treat- 

 ment. Consequendy, the mitotic capacity of meristematic cells was 

 destroyed. Following X-irradiation, bulbs were placed over colchi- 

 cine, and typical c-tumors formed with no evidence for several days 

 thereafter of c-mitoses in these roots. We may conclude, therefore, 

 that enlargement occurs without a simultaneous division of cells. 

 Polyploidy following a c-mitosis is not necessary for tumor forma- 

 tion."'^ 



Swelling at the hypocotyl when seedlings were soaked in colchi- 

 cine gave the first evidence that tumors were in no way related to 

 c-mitosis or induced polyploidy. Although cells in the hypocotyl are 

 not meristematic, they are capable of elongating or expanding. Colchi- 

 cine causes an isodiametric expansion of cells much the same as among 

 cortical cells in roots. •"'- 



The tumor formation is proportional to concentration within cer- 

 tain limits.^^ Different species show different degrees of response to 

 the same concentration. Another factor is the sj)eciric moment when 

 seedlings are placed in colchicine. i^'" If the seedling has not yet elong- 

 ated, there is swelling throughout the entire hypocotyl. But the seed- 



