HARMFUL SOIL CONSTITUENTS 163 



supported in a notched cork which fitted closely in the wide 

 mouth bottle. The first experiment was made using mannite 

 dissolved in pure distilled water, as a culture solution. The 

 mannite was used in concentrations of 10 to 200 parts per mil- 

 lion, and the plants were grown in the "solutions from January 

 12-25. Growth in some of the mannite concentrations was 

 about equal to that in pure distilled water, some of the cultures 

 produced larger growth and others made less growth than in 

 distilled water. 



A large experiment was made using nutrient solutions com- 

 posed of calcium acid phosphate, sodium nitrate, and potassium 

 sulphate. These salts were used in solution singly, in combina- 

 tion of two, and of three salts, in all possible proportions, varying 

 in 10 % stages. In this set there were 66 solutions, which were 

 used as a control and to a second set of 66 solutions similar in 

 composition was added 100 p.p.m. of mannite. The composi- 

 tion of each of the 66 solutions is given in the second, third and 

 fourth column of table 1. Wheat plants grew in these solutions 

 from February 14 to February 26. The solutions were changed 

 every third day and replaced by fresh solutions of the same 

 composition. These solutions were analyzed for nitrate after 

 the plants had grown in them. They were also tested for ni- 

 trites and ammonia, to determine if decomposition was going 

 on. In table 1 are given the composition of the culture solu- 

 tions together with the green weight produced in the solutions 

 without mannite and with 100 p.p.m. of mannite. 



• The total weight produced in the 66 solutions without mannite 

 was 151.2 grams against 142.4 grams for the cultures containing 

 mannite. While the total growth was less in the mannite cul- 

 tures than in the control solutions, a close examination of the 

 table shows that in those solutions containing no phosphate, 

 Kos. 56 to 66, the growth was larger in the mannite solution, 

 with the exception of one, No. 56, than the control solutions. 

 The mannite caused less growth in nearly all of the other cultures 

 which contain phosphate in some amount. Among the 46 so- 

 lutions containing phosphate only ten of the mannite solution 

 produced larger growth than their checks. The roots of the 



