Results of Water Culture Experiments. 429 
supply of any one of such salts should be below a certain amount, such 
a salt may act as a limiting factor on growth. When this is the case an 
increase in salt supply will bring about a corresponding increase in growth. 
On the other hand, if some other factor is limiting growth, an increase in 
salt supply will not result in any increase in growth. 
If through the limiting. action of any factor, as for example temperature, 
the rate of growth is small, we may therefore expect plants to be unaffected 
over a wide range by the total amount of nutrient salt supplied. When, 
however, owing to increase in the value of this factor, a higher rate of 
growth is possible, we may expect the limiting action of quantity of salts 
supplied in a given time to be present over an increased range of con- 
centrations. 
Results already published appear to show this very clearly. Cultures 
were grown by the writer, and more recently by Dr. Brenchley, in solutions 
of the same relative composition but of different concentrations (1, •!•, -g 1 ^). 
Considering only those cultures in which the nutrient solutions were 
frequently renewed, we may take for granted that in the cases where the 
highest concentration was employed the salt supply was not limiting . 1 
When the rate of growth in the strongest solution is rapid, as in 
Dr. Brenchley ’s experiments, although the growth is about the same when 
the total supply of salts is reduced to yet further reduction in salt supply 
causes a marked reduction in growth. 
In the experiments of the writer the rate of growth in the highest 
strengths of solution was not so great as in the case of Dr. Brenchley’s 
plants, probably owing to temperature acting as a limiting factor. Here 
there was no marked reduction in growth until a much lower strength (2V) 
of solution is reached. 
Again, in the preliminary experiments of the writer made with Rye 
during the winter months, when growth was still slower, there was no 
significant lowering of growth even in the case of plants growing in solutions 
of & the concentration of the strongest. 
The following table summarizes the results of both writers : 
Grammes KN 0 3 
supplied in highest 
strength of solution. 
Growth ( dry matter in grammes ) 
in solutions of relative strength. 
Observer . 
Plant. 
io*8 
1 
0-059 
1 
5 
0-072 
i 
1 0 
0-059 
1 
•2TT 
0-060 
Stiles. 
Rye. 
io-8 
0-628 
0*622 
o -555 
0 - 47 1 
Barley. 
9 ’° 
4-00 
3*65 
2-80 
1.83 
Brenchley. 
>> 
9-0 
5*77 
4 ’ 5 ° 
2-74 
1-97 
>5 
>> 
7-8 
6-46 
6-04 
3-09 
1 • 78 
9 > 
1 This is indicated by Dr. Brenchley’s observation that 25 per cent, of the original supply of 
nitrate was still left in such a culture solution that was unchanged for eight weeks. However, in this 
case there was almost certainly limitation of growth due to other factors, as, for instance, accumulation 
of carbon dioxide in the culture solution. 
