84 Brenchley . — Effect of Concentration of the Nutrient Solution 
Third Series. 
Seeds sown, April 16. 
Plants put into solutions, April 26. 
Plants harvested, June 14. 
Solutions changed ‘ frequently every four days. 
Solutions changed ‘ once May 20. 
This series was started rather late in the season, so that in some ways 
the plants exhibited more variability than in the earlier experiments. With 
frequently changed solutions the 
life-histories were much as usual ; 
in the N-plants the roots were 
inclined to be rather short and 
bushy from first to last, and were 
well supplied with the typical 
thick rootlets ; for about a month 
the N/5-plants looked stronger 
than the N, but this did not con- 
tinue ; in lower concentrations a 
rapid falling off of growth was 
exhibited. The red coloration 
did not appear in the stems, but 
the lower leaves were dead in 
every case. When the solutions 
were rarely or never changed, the 
plants in the two lower concen- 
trations made little or no head- 
way for a long time. Root de- 
velopment was checked almost 
entirely for three or four weeks, 
after which very long thin roots were produced. The shoots were also 
long and very thin, with little or no tillering. The sharp falling off in 
growth below the N/5 concentration, even when the solutions were changed, 
is well shown in the graph (Curve 3 and Table I). 
Curve 3. Mean dry weights of ten barley-plants 
grown in nutrient solutions of different concentra- 
tions. Dotted lines show limits of probable error. 
(April 26-June 14.) 
Discussion of Results. 
An examination of the figures and curves of dry weight in all three 
series shows that, however the solutions are treated, there is a steady decrease 
in the dry weights of the plants as the strength of the nutrient solution gets 
less. This decrease in weight is very considerable and is always outside the 
limits of experimental error. The results run in the same direction in all the 
experiments, the differences being accentuated in the sets grown later in the 
year, when growth is more rapid. It is noticeable that the drop in dry 
weight from N to N/5 is far less when the solutions are changed frequently, 
