584 The Philippine Journal of Science 1920 
pheres and then diluting this to give the concentrations required. 
The assumption is here made that the ionization constants for 
the salts are the same for the lower and higher concentrations 
as they are for the solution having an osmotic value of 1.60 at- 
mospheres. This method, therefore, is not strictly accurate. 
The error thus introduced is practically negligible for the solu- 
tions having values below 1.60 atmospheres. For the higher 
concentrations, freezing-point determinations indicated that this 
error gradually increased with the total concentration until it 
amounted to about 8 per cent. Thus solution T1R1C1, planned 
to have an osmotic value of 7.00 atmospheres at 25° C., proved 
by the freezing-point method to have an actual value correspond- 
ing to 6.50 atmospheres at 25° C. Since the purpose of this 
series was to study only the general relations between the growth 
of the plants and the total concentration, the error just alluded 
to may be disregarded. 
RESULTS OF SERIES IV 
Appearance of the plants . — Most of the morphological modi- 
fications of tops and roots noticed in the preceding series were 
also observed in series IV ; but the longitudinal striping of 
leaves and branching from the base of the stem were not seen 
in this series. Root development was retarded in the higher 
concentrations, both primary and secondary roots being thick 
and short. In the lowest concentrations the roots were long, 
slender, and flexible in appearance. Roots in the corresponding 
concentrations of cultures T7R1C1, T2R4C2, and R5C24 were 
about equal in development; but those in the T1R1C1 cultures 
were all greatly retarded. With all of the sets of salt propor- 
tions, the greenness of the plants decreased with decrease in 
concentration of the nutrient solution. The greenest plants 
were those having the T1R1C1 salt proportions; those in the 
R5C24 and T2R4C2 proportions were somewhat lighter in shade, 
and those in the T7R1C1 proportions were much lighter. Mag- 
nesium injury was not observed in any of the T7R1C1 cultures. 
Only one plant in the R5C24 cultures showed injury, this occur- 
ring in the 5.50-atmosphere concentration. Slight injury was 
observed in the T2R4C2 cultures in the 5.50-, 4.50-, and 2.50- 
atmosphere concentrations. Severe injury, with coiling of the 
leaves, was observed in all concentrations with the T1R1C1 salt 
proportions, the more severe injury appearing in the higher 
concentration. 
