NUTRIENT SOLUTIONS AND WATER CULTURES. 11 



require much more than 25 to 30 parts per million of SO 4 , since a 

 much larger amount was at their disposition during the whole period 

 without any larger amount being absorbed. These two solutions, 

 Nos. 7 and 8, containing 87 parts per million of SO 4 and 63 parts 

 per million of potash, respectively, show very clearly to what extent 

 selective action is practiced by the roots. At the end of the experi- 

 ment all of the potash had been taken up by the plant, while only 

 30 parts per million of SO 4 were thus absorbed. 



Solutions 5 and 6 show the same selective process going on in the 

 case of potassium chlorid. These solutions contained at the begin- 

 ning of the experiment 79 parts per million of the potash ion and 71 

 parts per million of the chlorid ion. At the end of the experiment 

 no potash was found in the solution, indicating that the plant had 

 absorbed the whole of this element, while 35 to 38 parts per million 

 of chlorid were still present. These results are at variance with 

 those obtained by J. de Rufz de Lavison, 1 who, after growing the 

 young seedling five days in twentieth-normal potassium-chlorid solu- 

 tion, found that the concentration of the solution was about equal 

 to that originally used. The probable reason for such a deduction 

 is that a potassium-chlorid solution of twentieth-normal strength 

 is equivalent to 3,700 parts per million, a solution so strong that even 

 if the plant did exercise a normal selective action of 30 to 50 parts 

 per million, it would be most difficult to detect such a change in a 

 solution of the concentration mentioned. 



The pans containing (1) the control, (2) the potassium-sulphate 

 solution, and (3) the potassium sulphate with calcium carbonate, as 

 given in Plate VIII, figure #,.show that the differences in the de- 

 velopment of the roots are marked and that the few plants selected 

 for the plates previously shown were not exceptions to the rule. In 

 every case the plants grown in the presence of lime presented a 

 healthier and more vigorous appearance than those grown in the 

 corresponding solutions without lime. 



TThile the tops of the plants grown in the culture solutions con- 

 taining calcium carbonate were larger and presented a much better 

 appearance than the others, yet their dry weight was not necessarily 

 greater; on the other hand, the dry weight of the roots was increased 

 in every case by the addition of calcium carbonate. 



Although the original seeds and the seedlings all contained sulphur 

 in organic combination, yet no weighable amount of inorganic sul- 

 phate was found in the ash of the plants, except in those to which 

 sulphate or sulphuric acid had been added. 



In the solutions to which calcium carbonate had been added the 

 carbon dioxid which was given off by the roots combined with the 



1 Du r61e e"lectif de la racine dans 1'absorption des eels. Comp. rend., 1910, 151: 675. 



