Feb. 17. I9I9 Effect of Barium and Strontium on Plant Growth 185 



however, the action of the barium carbonate was strongly toxic, as 

 shown by the failure of the plants in pot 1 1 . 



The efifect of the barium compound upon the growth of the cowpeas 

 is more strikingly shown in Plate 24. In figure A the pot on the right 

 is the control, which received no barium compound. The pot in 

 the middle received the same plant food as the control and 10 gm. of 

 barium carbonate in addition. The pot on the left received 5 gm. of 

 barium carbonate, but no calcium carbonate. It received the same 

 amount of tricalcium phosphate as the other pots. One object in mind 

 in this experiment was to ascertain whether there would be a tendency 

 on the part of the plants in this pot to substitute barium for calcium 

 in their growth. The peas germinated and came through the sand, 

 made a stunted growth for a few weeks, and then died. The difference 

 in the growth of the plants in the pot in the center and the one on the 

 left shows very strikingly the toxic effect of barium carbonate in the 

 absence of calcium carbonate. This experiment affords a very striking 

 example in the plants in the center pot of the protective action of calcium 

 carbonate on plants when grown in the presence of a toxic substance. 



Figure B of Plate 24 shows the effect of barium carbonate on the 

 growth of the roots of the cowpea plants grown in pots 1,2, and 8; the 

 plants on the right were the control and received no barium carbonate, 

 the plants in the center received 0.5 gm. of barium carbonate, and 

 plants on the left received 6 gm. of barium carbonate. It will be 

 observed that the plants which grew in the presence of barium carbonate 

 have made a markedly increased root growth over the control. It is 

 also to be borne in mind that the plants in the center received only 0.5 

 gm. of the barium compound, whereas the ones on the left received 6 

 gm. or 1 2 times as much as the former, thus indicating that a very small 

 amount of barium carbonate produces as great effect on the root growth 

 as much larger amounts. 



The compounds of strontium have many chemical and physical prop- 

 erties similar to those of barium and calcium. It was thought that a few 

 comparative experiments showing what effect like compounds of barium 

 and strontium might have upon the growth of plants would be of some 

 interest in this connection. Therefore in the series of experiments that 

 follow plants have been grown in the presence of both barium and stron- 

 tium compounds and compared with similar plants grown in the presence 

 of calcium compounds. 



OATS 



In a second series of experiments oats {Avena saliva) were grown in 

 sand under conditions similar to those in which the cowpeas v/ere grown 

 in the previous experiment, with the same basal plant food ration as 

 before. 



