94 Stiles.—Concentration of the Nutrient Solution and the 
Series 4. 
Cultures started May 1. 
Solutions changed May 25. 
Cultures harvested June 12. 
Concentration 
Dry weight 
Dry weight 
Total dry 
Probable 
Shoot 
of solution. 
of shoots. 
of roots. 
weight. 
error. 
root. 
grin. 
grin. 
grm. 
grm. 
1 
0*227 
0*085 
0*312 
o*oi 7 
2*7 
1 
5 
0*325 
0*103 
0*428 
0*021 
3-2 
1 
To 
o *377 
0*123 
0*500 
0*020 
3’ 1 
1 
So 
0*2826 
0*1287 
0*411 
0*018 
2*2 
Discussion of Results. 
The results recorded in the preceding section of this paper indicate 
that if the nutrient solutions in water-culture experiments are changed 
frequently, so as to maintain more nearly a constant composition of the 
solution, the concentration of the solution may vary considerably without 
producing much effect on the rate of growth of the cultures as measured by 
the dry matter produced within a given time. Below a certain concentra¬ 
tion, however, there seems to be an indication that the rate of growth 
becomes less, although this falling off is not very marked in the lowest con¬ 
centration employed in these experiments, and not nearly so marked as the 
falling off in the growth recorded by Hall, Brenchley, and Underwood for 
the same species growing in rather similar concentration. Indeed, the results 
concerning Rye and Barley recorded in the present paper are exactly described 
by Cameron when he states with regard to water-culture experiments with 
Wheat, ‘ that if a given ratio of mineral nutrients be maintained, relatively 
small effect is produced on the growing plants by varying the concentration 
over a wide range k 1 The recently published work of Tottingham 2 indicates 
the same conclusion. It should be stated that the plants which had pro¬ 
duced the least dry matter were quite healthy plants and showed no sign 
of weakening. 
Indeed, of the 160 plants grown none died nor showed any sign of lack 
of vigour when the cultures were stopped. 
It will be observed that when the nutrient solutions remain un¬ 
changed a marked depression of the rate of growth occurs. This can 
scarcely be due to lack of salt in the strongest nutrient solutions, although 
this cause may be operative in the solutions of weaker concentration. It 
might be caused by the harmful effect of excreta from the plant, but at 
present the existence of such toxic excreta cannot be regarded as definitely 
established. It might more probably be explained by the absorption of 
1 The Soil Solution, p. 70. 
2 Tottingham, W. E. : A Quantitative Chemical and Physiological Study of Nutrient Solu¬ 
tions for Plant Cultures, Physiol. Researches, vol. i, 1914, pp. 133-245. 
