86 Brenchley. — Effect of Concentration of the Nutrient Solution 
and N/20 plants in frequently renewed solutions were practically the same, 
within the limits of error, in all three experiments, showing that the same 
amount of growth had taken place in each case, whereas normally plants 
grown later in the season form much more dry matter, owing to the increase 
in the rate of growth, the N and N/5 plants in the three series being about 
50 per cent, heavier than those in the first series grown seven weeks earlier. 
This indicates that with the lower 
strengths the amount of growth 
was strictly limited by the quantity 
of food supplied, and that it was 
impossible for the plants to reach 
full development with such a re- 
stricted amount. 
In the single solution with 
wheat, the solution was frequently 
changed, and the plants were 
grown on for eight weeks. In 
this case again, a steady fall in 
dry weight occurred with decrease 
of concentration, but owing to 
lack of seeds it was not possible 
to carry the comparison so far as 
with barley. The drop is less 
marked with wheat, but this may 
be because it grows more slowly than barley, so that differences are less 
accentuated within the same limits of time, though they are none the less 
definitely marked (Curve 4 and Plate II, Fig. 4). 
Before proceeding to discuss the significance of these results further, 
it may be useful to summarize the effect of varying concentration of food- 
salts obtained by different workers. 
Worker. Plant. 
Brezeale .• Wheat 
Stiles Barley 
Hall and Underwood . . . Barley 
Brenchley Barley 
Brenchley Wheat 
Parts per million of Food-salts. 
75 °- 75 
growth similar. 
1,800 360 180 90 
v " shows 
growth similar. slight 
decrease. 
3,000 600 300 150 
steady decrease in growth. 
3,000 600 300 150 
growth marked 
possibly decrease 
much same in growth 
(solutions changed). 
3,000 600 300 150 
steady decrease in growth 
(solutions not changed). 
3,000 600 300 150 
steady decrease in growth 
(solutions changed). 
Curve 4. Mean dry weights of six wheat-plants 
grown in nutrient solutions of different concentra- 
tions. Dotted lines show limits of probable error. 
Solutions frequently renewed. (March 16-May n.) 
