Rate of Growth of Plants in Water Culture. 93 
Summarizing these results and taking the probable error into account 
the following numbers are obtained : 
Dry weight in grm. 
Concentration of 
Highest and lowest 
nutrient solution. 
numbers. 
1 
0*669 
0*587 
1 
3 
0*657 
0*587 
1 
To 
0*585 
0-525 
1 
20 
0*486 
0*456 
Thus the only mean dry weight which differs from the others by an 
amount exceeding the probable error is that of the cultures growing in the 
dilutest solution, and even here the difference is not very great. 
As the concentration of this particular solution is less in all essential 
things, except nitrate and iron, than the lowest strength of nutrient 
solution used by Hall, Brenchley, and Underwood, it is surprising that 
the difference in the dry weight between the cultures grown in this solution 
and those grown in the highest strengths should be so small. The numbers 
obtained by Hall, Brenchley, and Underwood are as follows: 
Dry weight. 
0*420 
0*244 
0*108 
0*068 
Concentration of 
nutrient solution. 
1 
1 
5 
1 
¥ 
20 
In order to determine whether an infrequent changing of the nutrient 
solutions influences the result, two further series of Barley cultures were 
grown in solutions which were seldom changed. In all other respects these 
cultures were conducted similarly to the others. They were done in sets of 
ten and the probable error of the mean dry weight of each set calculated. 
The numbers already given serve to illustrate the variation in dry weight 
obtained within one set, and so individual results are not given in the 
following tables. The results are as follows: 
Series 3. 
Cultures started April 30. 
Solutions changed May 11, %i. 
Cultures harvested June 9. 
Concentration 
Dry weight 
Dry zveight 
Total dry 
Probable 
Shoot 
of solution. 
of shoots. 
of roots. 
zveight. 
error. 
root. 
grm. 
grm. 
grm. 
grm. 
1 
0*332 
0*110 
0*442 
0*022 
3 *o 
1 
5 
0-3485 
0*1124 
0*461 
0*019 
3*1 
1 
10 
o -3437 
0*1046 
0*448 
0*01 2 
3'3 
1 
20 
0*189 
0*077 
0*266 
C«OI I 
2-5 
