[Vor. 7 
46 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
concentration represented by Pu 5.4 to Pu 7.1; frequently, 
however, it is 6.6 to 7.1. 
The experiments have been carried out in the greenhouse at 
different periods of the year, and represent, on the whole, à con- 
siderable range of environmental conditions. It has been 
impracticable to analyze these except in a very general way, or 
relatively. Wheat and corn have been employed in every series 
of experiments and Canada field peas in all series here reported 
except one. 
Under the most favorable conditions, the 3 solutions men- 
tioned above, without other modification, may all yield excel- 
lent growth. Plants grown in solution B are invariably of a 
deeper green, presenting a finer appearance, and the average 
of the growth quantities (green weight) is higher for wheat and 
eorn than in either of the other 2 solutions. In the unmod- 
ified solutions A and C the green weight of peas averages higher 
than in the unmodified solution B. 
Culture solutions prepared with monobasie phosphates may, 
however, exhibit a hydrogen ion concentration which is too high 
for the maintenance of the best growth under certain conditions, 
and especially is this true in the case of wheat. 
Solutions made with monobasie potassium or calcium phos- 
phate free from acid may, under certain conditions, yield max- 
imum growth quantities, but there is often considerable varia- 
bility in the duplicate cultures due to unknown factors. Certain 
grades of the phosphates mentioned—if not specially purified in 
the laboratory—exhibit a Py which may be distinctly toxic. 
Correction of the Pu to about 4.8 or 5.2 by means of NaOH or by 
the use, in part, of a dibasie salt generally affords increased 
growth. 
Under extreme conditions—effecting a high evaporation 
rate—it becomes more important to correct to the higher Ps 
exponent. Wheat, corn, and peas are sensitive in the order 
named to high hydrogen ion concentration. 
Usually, the addition to solution B of small amounts of dibasic 
potassium phosphate, of solid calcium carbonate, and of alu- 
minium hydroxide has given increased yields, often considerably 
above that of the unmodified solution. The results in the case 
of the aluminium compound are notable in the case of wheat 
