SOIL CONDITIONS AFFECTING PLANT GROWTH 91 



had been obtained by mixing i part of radio-active material 

 (2 mgs. Ra per ton) with 10 of soil. It isitrue that ^toklasa's ^ 

 results were negative (although in his other experiments radium 

 emanations increased growth to a marked extent), but this did 

 not prevent the introduction of radio-active fertilisers, and the 

 enterprising syndicates and companies concerned were by no 

 means loth to push their wares. These were investigated by 

 Martin H. F. Sutton,^ the experiments being made with 

 radishes, tomatoes, potatoes, onions, carrots, and marrows, 

 some grown in pots, others in plots out of doors. Eight 

 different radium residues were used, in addition to pure radium 

 bromide ; the dressings were so arranged that equivalent 

 quantities of radium were given in each case (j-^ grm. radium 

 bromide to i 5 lb. of soil : 2\ times this amount per sq. yard 

 to the plots). 



In no case was there any clear evidence of increased 

 growth, even the pure radium bromide seemed to be without 

 action. 



We are therefore left with the apparent discrepancy already 

 observed on p. 35. The work of the physiologists, assuming 

 it to be sound, indicates that radium emanation is capable of 

 stimulating certain cell activities. Sutton's results show that 

 such stimulus, if it exists, does not affect the final growth of 

 the plant. This discrepancy is periodically confronting the 

 agricultural investigator. Thus, Dr. Winifred Brenchley at 

 Rothamsted has failed to obtain increases in growth by supply- 

 ing plants with inorganic poisons which have been supposed 

 to stimulate certain cell functions in suitable dilutions. The 

 result opens up the prospect of an interesting discussion, but 

 it also shows the danger of arguing from a simple physiological 

 observation to a complex phenomenon like the growth of a 

 plant in soil. 



Zwaardemaker ^ has obtained some interesting results in 

 the case of animal organs which deserve close study by plant 

 physiologists. 



^ Chem. Ztg., 1914, 38, 841-844. ^ Messrs. Sutton's Bull., No. 6, 1916. 



^ yourn. Physiology, 1920, 53, 273, discussed by V. H, Blagkman in Annali 

 of Botany, 1920, 34, 299. 



