Dec. I, 1919 



Effect of Salts and Organic Extracts on Citrus Seedlings 2 7 



TOXIC LIMITS OF ALKALINE SALTS 



The toxicity of calcium hydrate, sodium hydrate, and sodium carbon- 

 ate was determined for lemon and grapefruit seedlings which showed 

 practically the same degree of resistance. The cultures in calcium hy- 

 drate solutions while under observation were kept in a large desiccator 

 containing quickhme. A concentration of 25 parts per million of cal- 

 cium hydrate or sodium hydrate gave stimulating results. When the 

 concentration of calcium hydrate was increased to 50 parts per million, 

 signs of distress were noted. Little growth took place at 80 parts per 

 million, and at 100 parts per million growth practically ceased. Here a 

 wide variation was noted among the seedlings. Occasionally a vigorous 

 seedling would withstand a concentration of 120 parts per million of 

 calcium hydrate. This was exceptional, however, and it may be said 

 that the citrus seedling will seldom tolerate 100 parts per million of cal- 

 cium hydrate. 



With sodium hydrate a concentration of 25 parts per million stimu- 

 lated the root growth, and concentrations up to 200 parts per million 

 were maintained with little harmful effect upon the plant. With 250 

 parts per million the growth was slight, while with 275 to 300 parts per 

 million growth practically ceased. With sodium carbonate it was neces- 

 sary to increase the concentration to 550 or 600 parts per million in 

 order to stop the growth of the seedlings. It is of interest to note that 

 a solution of this concentration would, on account of hydrolysis, contain 

 sodium hydroxid in approximately the same concentration as that rep- 

 resenting the toxic limit of sodium hydroxid. In other words, it is the 

 hydrolyzed portion of the sodium carbonate which mainly determines 

 the toxicity. 



Since calcium hydrate and sodium hydrate have nearly the same equi- 

 molecular weights, it follows that the hydroxyl concentration in the toxic 

 calcium hydrate solution is only about one-third that in the toxic sodium 

 hydrate solution. It is evident that the metallic ion is contributing also 

 to the toxicity. 



When organic matter (extracted from peat with ammonia) which is 

 acid in reaction and stimulating to root growth is added in the proportion 

 of 100 parts per million to a solution containing 400 parts per million of 

 sodium carbonate, a toxic body is formed that will kill the root tip of 

 the seedlings. (PI. 34, A-D.) This is not true, however, with organic 

 matter extracted from peat with water. This class of reactions appears 

 to be of importance in connection with the toxicity of alkaline soils and 

 will be made the subject of a later report. 



