May, 1922] TOTTINGHAM AND RANKIN NUTRIENT SOLUTIONS 27I 
Table i. Change of pH Values of Solution R8C1, Type III, Three-Salt Solution 
Cone. pH 
Usual (1.75 atm.) 4-i 
0.5 usual 4-3 
0,1 usual 5-3 
o.oi usual 5.4 
0.001 usual 5-5 
The same solution diluted to o.i its usual concentration was adjusted 
to pH values of 64 -and 7.5 by the addition of KOH. When used as a 
medium for germination, including preliminary soaking of the seeds and 
suspension on netting upon the flowing solution, this nutrient solution at 
pH 6.4 gave root systems but little superior to those obtained at pH 5.3. 
At pH 7.5, however, the roots elongated in a satisfactory manner, so that 
the seedlings were employed in a test described later. 
These results hardly agree with those of Hixon (4), who found pH 
values both below and above 6.0 favorable for elongation of roots in the 
germination of wheat. It should be noted, however, that his solutions were 
not renewed. Salter and Mcllvaine (14), employing the method of in- 
termittent renewal of nutrient solutions, reach conclusions directly opposed 
to ours, namely: 
Germination of the seed was found less sensitive to an acid reaction .... than was the 
subsequent growth of the seedling. 
Their criterion of growth, however, was green weight of seedlings. 
Their photographs of wheat seedlings show best root development at pH 
7.7. Inasmuch as wheat grows well at much lower pH values than 6.4, 
as shown by Duggar (3), and appears to be independent of hydrogen-ion 
concentration in yield of dry matter, at least in intermittently renewed 
solutions, as observed by Meir and Halsted (12) and by McCall and Haig 
(10), it seems possible that its peculiar sensitiveness to pH values during 
germination may be related to some factor inherent in the seed, such as 
the isoelectric points of its proteins. 
The adjustment here developed seems to offer a means of providing 
more uniform seedlings for different collaborators, by use of a common 
solution for germination, should it seem advisable to continue such practice. 
Comparison of Continuous with Intermittent Renewal of 
THE Nutrient Solution 
One of the fundamental desiderata of investigations with nutrient 
solutions is the avoidance of disturbing effects of the absorbing plant upon 
the concentrations and proportions of nutrients available to it. This 
point was stressed long ago by Nobbe (13) and has been re-emphasized by 
Hoagland (6). 
For the present purpose Shive's solution R5C2 was employed. The 
