158 
JOHN W. SHIVE 
the best growth (measured by dry weight) occurred with the same 
proportions of salts as those giving the best growth in the earlier 
work. While Tottingham reports an improvement of 1 1 percent over 
Knop's proportions, the corresponding improvement here shown was 
12 percent. This agreement between the two results becomes still 
more pronounced when it is noted that the two experiments were 
carried out in different years and at different seasons. 
Since the general problem of the salt requirements of plants 
largely remains to be studied, and since nutrient solutions will surely 
have to be employed in experiments bearing on this problem, it is 
quite essential that the standard solution used as a basis of comparison 
be as simple as possible and that it produce excellent growth of the 
plants. That distilled water is not suitable for use as such a standard 
is obvious from the fact: (i) that this medium removes salts from the 
plants, and (2) that the plants in pure water become visibly unhealthy 
after a few days and soon cease to grow at all. One phase of this 
matter has been dealt with by True and Bartletf^ and by True.^ It 
therefore seems highly desirable to devise a simpler solution than the 
four-salt mixture used by Knop and Tottingham, if this can be 
accomplished. An attempt was made in this direction, and the 
present announcement aims to state the main results in a preliminary 
way. A more complete account of this work will appear later. 
Combinations of three nutrient salts, which contain all the essential 
elements required for plant growth besides iron, and which do not 
precipitate when mixed in solution of th'e needed concentration, are 
comparatively few. The solution here employed contained mono- 
potassium phosphate, calcium nitrate, and magnesium sulphate; 
potassium nitrate is thus omitted from the Knop formula. These 
three salts contain all the essential elements except iron, and they 
dissociate in solution to form all of the ions present in the Knop- 
Tottingham four-salt solution. They do not readily precipitate when 
mixed in solution, and permit total concentrations suitable for plant 
growth. Thus the three-salt solution appears to be chemically 
adapted for the purpose in view. Growth tests are needed to show 
its suitability for supporting plant growth. 
2 True, R. H., and Bartlett, H. H. Absorption and Excretion of Salts by Roots, 
as Influenced by Concentration and Composition of Culture Solutions. U. S. Dep. 
Agr. Bur. PI. Ind. Bull. 231. 1912. 
3 True, R. H. Harmful Action of Distilled Water. Amer. Journ. Bot. i: 
255-273. 1914. 
