96 
Stiles.—Concentration of the Nutrient Solution. 
potassium and phosphate in the various solutions used in these experiments 
with the quantities found by Cameron to be present in the soil solution. 
Parts per Concentration of solution. 
io 6 of T 111 
J 1 5- TO 20 
K 2 0 552 no 55 28 
P 2 0 5 131 26 13 6-5 
Thus the weakest solution when first put in the culture jars was of the 
same strength in regard to potash and phosphate as that of the soil solution. 
This probably means that its average strength during the time it was in the 
culture bottles was somewhat less; and although the plants grown in this 
dilutest solution produced somewhat less dry matter than those in higher 
strengths, the difference was not great and the plants were perfectly 
healthy. 
Finally, it should be pointed out that such results as those here 
recorded cannot be regarded as in any way general. Although all the 
plants in one series were grown under apparently exactly the same con¬ 
ditions, yet it is possible that under a different set of conditions a different 
result might be obtained. Again, different species might show different 
effects in regard to concentration of the nutrient solution. It must be left 
for future work to deal with these questions. 
Summary. 
1. The variation over a fairly wide range of the concentration of the 
nutrient solution of Rye and Barley growing in water culture produces 
relatively little effect on the amount of dry matter produced. Below 
a certain concentration there appears to be a definite falling off in the rate 
of growth. 
2. The concentration of the soil solution as estimated by Cameron, low 
as it is, is yet high enough to produce healthy plants. 
3. Frequent changing of the nutrient solution of water cultures pro¬ 
duces decidedly better growth of the plants. 
4. It is necessary to calculate the probable error of the results obtained 
in experiments with water-cultures in order to determine the significance of 
differences between results from different sets of cultures. 
Botany Department, 
The University, Leeds. 
June 25, 1914. 
Soil solution 
according to 
Cameron. 
about 28 
about 7 
