i7, 6 Trelease: Salt Requirements of Wheat Plants 557 
these low areas lying in the lower left-hand corners of the 
triangles, denoting solutions having high proportions of mag- 
nesium sulphate, and low proportions of calcium nitrate and 
monopotassium phosphate. The general proportionality be- 
tween the transpiration and the dry yield reported by other 
workers was thus observed in these experiments. This rela- 
tion is of course to be expected, since the ability of a particular 
set of plants to transpire depends principally upon the leaf 
surface of the plants; this is measured approximately by their 
dry weight, and the amount of water absorbed is a measure of 
their transpiration. 49 
Water requirement . — The highest water requirement for tops 
(Table 4) was found to be that for culture T6R1C1, having 0.6 
of its total osmotic concentration due to potassium chloride. 
Three quite different cultures showed the lowest water require- 
ment for tops. These were cultures T1R5C2, T2R2C2, and 
T2R4C3. There is very little in common between these cultures, 
as regards the proportions of the salts. Triangular diagrams, 
omitted in this publication, have shown that areas of high water 
requirements for tops occur in all of the triangles ; that is, with 
all proportions of potassium chloride tested. These areas lie 
in almost all cases along the lower margins of the triangles, 
and are thus restricted to cultures having very low partial con- 
centrations of monopotassium phosphate. On the other hand, 
low water requirements are in general associated with high 
relative proportions of monopotassium phosphate. In a very 
general way, solutions which gave high water requirements of 
tops also gave high top yields and, conversely, those which gave 
low water requirements gave low top yields. No relation is 
apparent between high water requirement of tops and either 
water absorption or root yields. 
Turning now to water requirement of roots, it is seen that 
culture T2R1C3 showed the highest value, while culture T1R1C1 
showed the lowest value. High values were not found in this 
series for solutions having more than 0.4 of their total concentra- 
tion due to potassium chloride. There is no evident general cor- 
relation between either high or low values and the proportions 
of the various nutrient salts. A comparison of the triangular 
diagrams, representing water requirement of roots, with fig. 3 
has shown that there is a suggestion of an inverse relationship 
49 Livingston, B. E., Relation of transpiration to growth in wheat, Bot. 
Gaz. 40 (1905) 178-195. 
