Ocroner 25, 1918] 
reaction remained constant throughout the 
entire period. The data from a number of typ- 
ical experiments are presented below. H ion 
concentrations were usually determined colori- 
metrically, with the methods and indicators 
described by Clark and Lubs.? 
TABLE I 
Reac- 
Reactt 
Description of Time of eee After Cat 
Plant Solution Contact | ping, | tact with 
Py Plant, Py 
Barley grown|Complete 4 mos. 6.8 | 6.9 
to maturity.| nutrient 
Nochange of; 1500 p.p.m. 
solution , 
Barley 6 weeks| Complete lweek| 5.6 | 6.8 
nutrient 
2500 D.p.m.) 
Barley 7 weeks) Complete 22 hrs. 5.1 6.1 
nutrient 
1500 p.p.m. } 
Barley 7 weeks; Complete 36 hrs. 5.1 6.8 
nutrient 
1500 p.p.m. | | 
Barley 7 weeks} Complete 50 hrs. BO ie | Ook 
nutrient | 
5000 p.p.m. } 
Barley 7 weeks) Complete 96 hrs. 5.0 | 6.5 
nutrient 
5000 p.p.m. x 
Barley grown Complete 12 weeks) 6.8 | 6.5-7.2 
to maturity | nutrient 
300, 1000, | 
2500 p.p.m. | 
Chemical analyses of the solutions made it 
clear that the change in reaction had been the 
result of selective absorption from the various 
phosphorie acid anions, accompanied by an 
equivalent removal of positive ions. A marked 
regulatory absorption is apparent. 
Other experiments were made in which bar- 
ley plants were grown for seven weeks in 
favorable nutrient solutions and then trans- 
ferred (after thoroughly washing the roots in 
distilled water) to solutions of KCl, K,SO,, 
MgSO,, K,PO,, NH,Cl and NaNO,. The 
reactions of the solutions were tested after 
varying periods of contact from a few hours 
to forty days. In no case was a condition 
either of excessive OH ion or H ion concentra- 
tion produced, although absorption had been’ 
8 Clark, W. M., and Lubs, H. A., Jour. Biolog. 
Chem., Vol. XXV., No. 3, pp. 479-510, 1916. 
SCIENCE 
423 
active. The acid reaction when present was 
due to slightly dissociated acids, usually car- 
bonie, or to acid salts in the case of the NH,Cl 
solution. Possibly in some cases organic acids 
were formed. 
TABLE II 
ae}; , Reaction 
Salt Used. Time of vot Sait” EES | Pome 
(Concentration | Contact | Absorbed | ocrtact, | Heating 
duetivity) PH Py 
KOs. bak eee 39days| 42.6 5.3 6.5 
NaINOa! 2222 he ee 56.5 7.2 9.5 
MgSOriis) cee 16° 22.9 6.5 7.0 
Licis(0 iets habe 1GV Es 36.8 6.3 7.0 
REPO yew ne Lilet 33.0 7.5 — 
NERC Eee eke: 30.0 5.0 — 
Py original solutions (1) 10.3, (2) 5.7. 
Barley plants grown seven weeks in complete 
nutrient solutions. 
Very striking is the change induced in the 
K,PO, solution. From a condition of intense 
alkalinity the solution became approximately 
neutral. The NH,Cl solution retained an 
acid reaction. This would necessarily be the 
case as long as any NH,Cl remained un- 
absorbed. The H ion concentration was 
slightly increased after contact with the plant, 
but less than would occur if even 1 p.p.m. of 
residual HCl were formed. Analysis of the 
solution showed a considerable absorption of 
both ions, but about 5 per cent. more NH, 
than Cl was removed. The balance was re- 
stored, however, by the excretion from the 
plant of equivalent quantities of other bases, 
chiefly calcium. There is no evidence that 
NH,OH8 was absorbed with the formation of a 
residue of HCl. At least neither the analysis 
nor the reaction indicates that the absorption 
took this course. 
After boiling the NaNO, solution gave an 
OH ion concentration similar to that pro- 
duced by the hydrolysis of Na,CO,. The 
residual solutions of NaNO, and KCl were 
analyzed with the following results. 
From the above it may be inferred that part 
of the NO, was removed simultaneously with 
an equivalent quantity of Na, but more NO, 
than Na was absorbed, HCO, ion entering or 
being formed in the solution to restore the 
