NUTRIENT SOLUTIONS AND WATER CULTURES. 13 



Effects of sodium nitrate. By reference to Plate III, a marked 

 difference will be noted between the distilled water control and the 

 distilled wadT with calcium carbonate, a difference much greater 

 than was shown in growing the first crop (see Plates I and II). It 

 will also be noticed from Table 3 that the acidity of the solution ha.- 

 increased threefold since the first cropping. Solution 3, Table 3, con- 

 taining sodium nitrate, which was alkaline after the first cropping, 

 ha- now also become acid. The sodium evidently either was ab- 

 sorbed by the plant or was neutralized by some organic acid. Solu- 

 tions 2 and 4, of course, remained alkaline. 



Relative effects of potassium chlorid and hydrochloric acid. In 

 Plate III, figure 5, the relative effects of potassium chlorid and 

 hydrochloric acid are again shown. The plants grown in the potas- 

 sium chlorid solution, which, when the second crop was sown, con- 

 tained no potash but a considerable amount of acid, made prac- 

 tically no root growth and a very poor leaf development. On the 

 other hand, the 1 plants grown in the hydrochloric-acid solution which 

 contained only one-eighth as much acid made a much better growth 

 both in roots and tops. 



Relative effects of potassium sulphate, sodium nitrate, and sul- 

 phuric acid. In Plate IV, figure a, are shown the residual effects of 

 the potassium sulphate and sulphuric acid. What has just been 

 said of the potassium-chlorid plants and the hydrochloric-acid plants 

 is in the main true of the potassium-sulphate plants and the sul- 

 phuric-acid plants also. Figure l> illustrates the residual effect of 

 sodium nitrate and potassium sulphate used singly and in com- 

 bination. 



COMPARISON OF THE FIRST AND SECOND CROPS. 



A striking difference will be noticed between the plants grown in 

 the potash solutions in the first and second crops, when no calcium 

 carbonate was present. The plants in the first crop had practically 

 as much acidity to contend -with during the latter days of their 

 growth as the plants of the second crop had during the first few 

 days of their growth, yet the first crop was much better than the 

 second crop. This difference was not due to the fact that the second 

 crop was deficient in potash, for the control pans containing calcium 

 carbonate but no potash gave excellent plants. It is to be noted that 

 the first crop had to contend only with a gradually increasing amount 

 of acidity due to the absorption of potash from the solution in which 

 it was growing, and it was therefore able to accommodate itself and 

 to endure much more acidity than if it had been placed in the 

 stronger acid solution at first, as was done in the case of the second 

 crop. It has been shown by Mr. Jensen, of the Bureau of Plant 

 Industry, in a piece of unpublished work, that the enzymic activity 



