it, 6 Trelease: Salt Requirements of Wheat Plants 593 
concentration, between the limits 1.60 and 7.00 atmospheres. 
The omission of potassium chloride did not alter the relationship 
between concentration and absorption for concentrations lying 
between these limits. 
The graphs for the T7R1C1 cultures and the T1R1C1 cul- 
tures both show perfectly definite maxima at 1.60 atmospheres. 
Above this concentration, water absorption bears an approxi- 
mately linear relationship to concentration. 
The most interesting portions of all of these graphs are those 
between the concentrations 1.60 and 7.00 atmospheres. It will 
be seen that the slopes of the T2R4C2 and R5C2^ graphs are 
about the same. But the slopes of the T7R1C1 and T1R1C1 
graphs are much less steep. Thus changes in concentration in 
the T7R1C1 and T1R1C1 sets of proportions (both of which were 
unfavorable media at all concentrations) produced much les's 
marked changes in water absorption than did similar changes 
in the very favorable T2R4C2 and R5C2i solutions. 
By comparing figs. 10 and 11 it will be seen that for cultures 
T2R4C2 and R5C24, between 1.60 and 7.00 atmospheres at least, 
water absorption is a good measure of top yield, and appears to 
depend principally upon the size of the plants. But for the 
T7R1C1 and T1R1C1 cultures, water absorption does not vary 
in the same way as do top yields. In both of these sets of 
cultures absorption decreases with increasing concentration 
between 1.60 and 7.00 atmospheres, while dry weight of tops 
increases with concentrations of from 1.60 to 3.50 (for T7R1C1) 
and to 4.50 (for T1R1C1) atmospheres and then decreases. 
Thus, as the concentration changes from 1.60 to 3.50 or 4.50 at- 
mospheres, top yields increase while water absorption decreases. 
The difference in amount of water absorbed in this case is not 
at all a measure of the change in dry weight. 
Water requirement . — As shown in fig. 12, a decrease in water 
requirement of tops accompanies an increase in the concentra- 
tion of the culture medium. This is true for the T2R4C2 and 
R5C24 cultures throughout the whole range of concentrations 
studied; while for the T1R1C1 cultures it holds only between 
1.00 and 7.00 atmospheres, and for the T7R1C1 cultures only 
between 1.60 and 7.00 atmospheres. This decrease approximates 
in most cases a straight line ; though, for a given change in con- 
centration, there is apparently a more rapid decrease in water 
requirement with the lower concentrations than with the higher. 
This is especially marked for the T2R4C2 and R5C2| cultures, 
between the concentrations 0.50 and 1.60 atmospheres. 
