432 
Stiles. — On the Interpretation of the 
Relative concentration of solution. 
Series 1. 
1 
1 
5 
1 
"i 0 
1 
2 0 
Never changed .... 
I'OOO 
1-000 
1*000 
1*000 
Once changed 
1*274 
1 *443 
i *493 
1 *628 
Frequently changed . . . 
1*520 
2*600 
3*386 
4 - 05 1 
Series 2. 
Never changed .... 
I *ooo 
1*000 
1*000 
1*000 
Once changed 
i*i 88 
1*319 
1*404 
i* 33 2 
Frequently changed . . . 
I *35 2 
2*548 
2*936 
3*747 
Series 3. 
Never changed .... 
1*000 
1*000 
1*000 
1*000 
Once changed 
1*250 
1*641 
1*251 
i *759 
Frequently changed . . . 
2*102 
3*748 
5*970 
10*73 
It will be observed that whereas the growth of culture in the strongest 
solutions was only improved from 1*4 to 2*1 times by frequently changing 
the solutions, in the most dilute solutions frequent renewal of the culture 
medium brought about from 4 to nearly 11 times as much growth. It 
strongly suggests that if the solutions had been changed still more fre- 
quently the rate of growth would have been still higher. The results 
indicate clearly that no conclusions whatever can be drawn from such 
observations as to the effect of varying concentration of the solution. They 
indicate that in the lowest strengths the salt supply was deficient and 
required very frequent renewals. In other words, the actual concentration 
soon fell below that of the initial concentration after renewal of the solution. 
Again, Dr. Brenchley states that for a considerable time all her 
plants grew as far as the eye could judge at equal rates, but that after 
that time those in the diluter solutions grew less rapidly than the others. 
This suggests that iii this later period of growth the plants are so large 
that the nutrient salts supplied in one lot of diluter solution are no 
longer sufficient for the growth that other factors would allow. The rate 
of growth is limited, not because of the concentration of the solution, 
but because the salt; supply is not kept up constantly. 
The difference between the rate of salt supply and the concentra- 
tion of the solution supplied at definite intervals may be made clear 
by considering an extreme case. If an adult oak-tree were grown in 
a litre of a dilute nutrient solution, supposing such a thing to be possible, it 
is quite clear that it would not require many minutes for the exhaustion of 
the food supply. If the solution were renewed every four days, salt supply 
would still limit growth exceedingly. But if it were supplied with a litre of 
the same nutrient solution for every square millimetre of absorbing surface, 
it would take a much longer time for the food supply to be exhausted, and 
if the solution were renewed every four days it is conceivable that the salt 
supply would not limit the growth. It is obvious that in the first case 
it would be erroneous to ascribe limitation of growth to the concentration 
of the external solution. Yet this is in effect what Dr. Brenchley does. 
It is clear from the writer’s experiments, and it is indicated also by the 
