RESULTS WITH PURE SOLUTIONS. 



EXPERIMENTAL METHODS. 



The methods used were described at considerable length in two 

 previous publications upon this subject." It suffices here to state that 

 the effect upon the rapidly elongating portion (10 to 20 mm.) of the 

 tips of the radicles of young seedlings was alone studied, inability to 

 further elongate when transferred to pure water after twent} 7 -four 

 hours' exposure to the salt solution being taken as an indication that 

 the concentration used was fatal to the root tips. The strength of 

 solution which permits the root tips of about half the total number 

 of seedlings used to survive this test is taken as the critical concentra- 

 tion. 5 The results are stated throughout in terms of fractions of 

 normal solutions. 



RESULTS WITH PURE SOLUTIONS. 



RESULTS WITH MAIZE (ZEA MAYS). 



Table I. — Limits of endurance of maize seedlings of salts of sodium and magnesium. 



Salts used. 



Critical con- 

 centrations. 



Salts used. 



Critical con- 

 centrations. 





0. 015 normal 

 . 04 normal 

 .05 normal 

























RESULTS WITH COTTON (GOSSYPIUM). 



The Jannovitch Eg}^ptian variety of cotton ( Gossypium barbadense) 

 and the Griffin Upland variety of cotton (G. Mrsutum) were selected 

 for these experiments. 



Kearney and Cameron, in Eeport No. 71, IT. S. Dept. of Agriculture, pp. 13 to 

 18; and Harter, in Bui. 79, Bureau of Plant Industry, U. S. Dept. of Agriculture, pp. 

 16 to 23. 



&The objection has been made to this method that the period of growth is too 

 short and that the effect upon the root tip does not necessarily represent the effect 

 upon the plant as a whole. Since, however, the purpose of these experiments is 

 merely to obtain a simple and ready means of comparison of the toxicity of different 

 salts to different plants under identical conditions and not a measure of the absolute 

 limit of concentration that will permit the growth to maturity of plants of a given 

 species, it is believed that the method used answers every purpose of this investiga- 

 tion. When the period is extended and the effect upon the whole plant is taken 

 into consideration so many disturbing factors are introduced that reliable results 

 become difficult if not impossible. Furthermore, since the conditions of these 

 experiments are confessedly artificial — pure salt solutions rarely, if ever, occurring in 

 nature — little would be gained by working out the limits of endurance for the entire 

 plant during a long period of growth. In the experiments with soil cultures now in 

 progress the effect of the salts upon the growth of the whole plant during a period 

 of several weeks is taken into account. 



