on the Growth of Barley and Wheat in Water Cultures, 79 
of the operator, and for that reason, if for no other, they have a special value 
of their own. 
During the season of 1915 a number of water-culture experiments have 
been made to see if further light could be obtained as to the effect of vary- 
ing concentrations of nutrient solutions upon growth, barley being used 
as the test plant in the three main series, wheat being grown in one case 
only. Four strengths of nutrient salts were used, N, N/5, N/10, N/20, the 
N-solution being that in general use in the laboratory, containing— 
Potassium nitrate 
Magnesium sulphate 
Potassium di-hydrogen phosphate 
Sodium chloride 
Calcium sulphate . 
Ferric chloride 
Distilled water 
1 grm. 
°*5 > > 
°'5 » 
°*5 j > 
°*5 » 
0-04 „ 
to make up one litre. 
The range of concentration was thus approximately 3,000, 600, 300, 
150 parts of food-salts per million, containing potassium, phosphate, and 
nitrogen as in the following table : 
Parts per Concentration of Solution 
million of 
N 
N /5 
N/10 
N/20 
k 2 o 
640 
128 
64 
32 
p 2 o 5 
204 
4 1 
20.5 
10.25 
N 
13 8 
28 
H 
7 
All the usual precautions were taken ; the bottles were thoroughly 
washed, new corks were used in every case, the water was obtained from 
a silver still which was kept scrupulously clean and polished, and the food- 
salts were uniform all through the experiments and were weighed up 
separately for each unit of ten plants. 1 The barley was a pure strain 
of c Plumage ’ obtained from Mr. Beaven, and the seeds were all graded 
between 0-05 and 0-06 grm. to reduce individuality as much as possible. The 
wheat was a pure line of ‘ Persian ’ wheat obtained through. the kindness of 
Dr. N. Vavilov of Moscow; these seeds had to be sown without grading, as 
the supply was very limited. 
In each experiment with barley 120 plants were grown in units of ten. 
(1) All concentrations (N, N/5, N/10, N/20), the solutions being 
changed regularly every four days. 
(2) All concentrations, the solutions being changed once, exactly half- 
way through the experiment. 
(3) All concentrations, the solutions being never changed. 
Great care was taken of the roots when the solutions were being 
changed. While the bottles were refilled, one by one, the plants were 
removed, and the roots laid in a saucer containing a little solution corre- 
1 The salts used were Kahlbaum’s ‘ for analysis \ and the stock was specially reserved for this 
experiment in view of the impossibility of replacing them at the present time. 
