308 BOTANICAL GAZETTE [may 
The initial Py values of these solutions in the order given are 
3.6, 3.7, 3.6, and 4.3, while McCatt and Haac’s values are 4.1, 4.1, 
4.3, and 4.7 in the same order. Disagreements of this kind are 
to be expected, of course, because of the different methods employed 
in determining the Py values and in the preparation of the solutions, 
variations in the degree of purity of the salts used, differences in 
the temperatures of the solutions at the time when the measure- 
ments are made, etc. A good example of such discrepancies appears 
in the Py values of a series of the Livincston-ToTTiINGHAM solu- 
tions of type I as determined by McCatt and Haac and by MEIER 
and HAtsTEAD. ‘These authors do not agree upon a single solution 
of a complete series of twenty-one, the values determined by the 
latter authors always being considerably but uniformly higher than 
those determined by the former. 
It will be observed from the data of table IV that the maximum 
reaction changes produced by the plants during the fifty-two 
hour period of contact with the LivincsTon-TorrINGHAM solu- 
tions with low initial Py values are always considerably greater 
than are the corresponding changes in the solutions with higher 
initial Py values, since the final Py values of all these solutions 
show no very marked differences. Experience with these type- 
solutions has shown that the maximum reaction changes which 
young wheat plants are capable of producing in them finally 
always brings the Py values of the solutions very close to the 
neutral point, regardless of the initial Py values, although the . 
time required to accomplish this may vary considerably with the 
different solutions, owing to differences in their buffer properties. 
As has previously been shown (6), the direction of the reaction 
changes of the modified TorrmycHam solutions during contact 
with the roots of the young wheat plants is usually the opposite 
of that of the Livincston-TorrincHam solutions and of the 
unmodified TorrincHaM (18) solutions under similar conditions. 
It will be observed, however, that the maximum reaction changes 
produced in these solutions by the plants during the fifty-two 
hour period of contact are not very great, the change in the H ion 
concentration of both solutions here considered being from Pu =4.8 
to Py=4.2, although the total osmotic concentration value of 
these solutions is only 1.0 atmosphere. » 
