90 
Brenchley . — Concentration of Water Cultures. 
other observers. The action of different high concentrations of constant 
balance has not yet been determined, and it is uncertain whether there 
is an optimum strength, above and below which growth falls off, or whether 
there is a range of concentrations between which the plants will make 
equally good growth. It seems evident, however, that if water cultures 
with wheat and barley are carried out under advantageous growth- 
conditions, complete and maximum growth cannot be obtained in 
a solution containing the amount of potash and phosphoric acid (K 2 q 
28 p.p.m., P 2 0 5 7 p.p.m.) stated by Cameron to exist in the soil solution. 
Rothamsted, 
October , 1915. 
EXPLANATION OF PLATE II. 
Illustrating Dr. Brenchley’s paper on Concentration of Water Cultures. 
Fig. 1. Photograph showing the growth of barley-plants in water cultures when solutions were 
frequently renewed. Concentration of solutions, N, N/5, N/10, N/20. Series II. 
Fig. 2. As above, but solutions changed once only. Series II. 
Fig. 3. As above, but solutions never changed. Series II. 
Fig. 4. Photograph showing the growth of wheat-plants in water cultures when solutions were 
frequently renewed. Concentration of solutions, N, N/5, N/10, N/20. 
