Vol. 7 
18 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
cultures not included in the previous series. Attention may be 
drawn to the inclusion of cultures in which the hydrogen ion 
concentration of the A series was increased by slight additions of 
phosphoric acid, as in Ax 1/, Ax 3/, likewise in solution A the 
substitution for one-half the quantity of the monobasic salt by 
an equivalent of the dibasic potassium phosphate, this being 
designated AxM. In the B solution there were also introduced 
cultures to which relatively small amounts of phosphoric acid 
were added, Bx 1/, Bx 2/, and Bx 5/, also one culture in which 
was included 1 gm. of solid calcium carbonate, BxCa. A fresh 
quantity of the salt in the case last mentioned was introduced 
with each change of solution. A general examination of the 
total green weight quantities in the case of wheat indicates that 
under the conditions of this experiment the maximum growth 
quantities were obtained with the B solution. Small amounts of 
phosphoric acid or of either phosphate (BxK;/10 and BxK/10) 
gave an increase in growth over the unmodified solution, and 
within the range of hydrogen ion concentration which prevailed 
in this culture solution relatively little influence was exerted by 
changes in Px except in the case of one culture, Bw 5/, where 
the hydrogen ion concentration was increased to Py 3.2. On 
the other hand, with the A solution it is clear that the addition 
of alkali to the unmodified solution is generally beneficial, at 
least at concentrations up to and including Aw /10, in which 
culture the Py exponent is raised to 5.8. Further addition of 
alkali gives a falling off in the growth quantities. In the culture 
Aw /20 where the hydrogen ion concentration is Py 6.3, pre- 
cipitation occurred and a marked decline in growth is apparent, 
although the reaction of the medium is the same as that which 
in the B series promoted an amount of growth approaching the 
maximum. This is one of the many indications pointing clearly 
to the probability that the most favorable hydrogen ion con- 
centration, or range of concentration, for a particular nutrient 
solution does not necessarily correspond to that which is most 
favorable with the solution of entirely different constitution. 
The growth quantity recorded for Aw 1/ is not strictly in line 
with the discussion above. The duplicates differed consider- 
ably. We have here, of course, two factors involved: (1) 
increase in acidity, and (2) slightly increased PO, concentration. 
