306 BOTANICAL GAZETTE © - fay 
The initial Py values of all the other solutions range between 4.0 
and 4.8. 
The Py values of CRoNE’s and of Sacus’s solutions remained 
practically unaltered during the entire period of contact with the 
plant roots. This is probably what might be expected, since the 
initial Py values of these solutions lie close to the neutral point, 
and since the maximum reaction change which the wheat plants 
are capable of producing in any of the solutions whose formulae 
appear in table I finally brings the H ion concentrations of these 
solutions very close to this point, either slightly below or slightly 
above a Py value of 7.0, regardless of the initial H ion concentrations 
of the solutions. 
The various solutions exhibit marked differences in the rates 
of reaction change in contact with the plant roots under similar 
experimental conditions. Of the solutions with initial Py values 
below 5.0, SHIVE’s solution R,C, exhibited the highest resistance 
to reaction change, while TorrincHam’s solution T,R,C, showed 
only slightly lower buffer properties as indicated by resistance to 
reaction change produced by the plants during the fifty-two hour 
period of contact. On the same basis the solutions of SCHREINER 
and SKINNER (16), and of HARTWELL, WHEELER, and PEMBER (5) 
possess relatively low buffer properties. With respect to the solu- 
tions here considered, it appears in general that the resistance 
offered to reaction change resulting from contact with the roots 
of growing plants is dependent largely upon the volume-molecular 
proportions of the soluble phosphate salts contained in the solu- 
tions. Thus SuHIve’s solution R,C,, which contains the highest 
proportion of dihydrogen potassium phosphate, exhibited the 
highest buffer properties. This is in entire accord with the observa- 
tions of McCatt and Haac (10), and of Meter and Hatsteap (11). 
In the present experiment, however, there is one striking exception 
to this general rule as exhibited by the solution of BrrNeR and 
Lucanus (1), which has a volume-molecular proportion of di- 
hydrogen potassium phosphate equal to that in TOTTINGHAM’S 
solution T;R,C,, and about two and one-half times higher than that 
in Knop’s (7) solution or in Prerrer’s (12) solution, yet these 
solutions showed a higher resistance to reaction change as influ- 
