Aug. i5 ,1925 Studies on Isoelectric Points for Plant Tissue 397 
f ;ested by the differences found in the position of the isoelectric point 
or P 0 t a fo-tuber tissue, as defined by the water absorption in different 
buffer mixtures. 
Whatever may be the ultimate complete and correct explanations 
of these writers’ data, theconception of the plant cell as an amphoteric 
colloid is one which will prove increasingly valuable. Pearsall and 
Priestley (4), and Weber (11), have suggested theories for the exist¬ 
ence or formation of meristem based upon such a conception. Ar¬ 
rhenius GO, in studying the ammonia, nitrate and total nitrogen 
content of soils of varying natural hydrogen-ion concentration, found 
that while the total nitrogen was rather constant in amount, the 
ammonia content was at its maximum in the acid soils and the nitrate 
in the alkaline soils. When plotted against the P H of the soil, the two 
curves for nitrates and ammonia content intersect near P H 6.5. This 
is what we should expect, if plants absorbed ions as they are taken up 
by an ampholyte with an isoelectric point near P H 6.5. Nitrate, as 
an anion, would be absorbed to the greatest extent from soils more 
acid than P H 6.5, and ammonia, a cation from soils more alkaline 
than P H 6.5. The maximum amount of nitrate would be left in 
alkaline soils and the maximum amount of ammonia in the acid soils. 
The isoelectric points given in this paper for potato-tuber tissue 
and soy-bean root tips are close to this value. 
Speculation, however, seems to the writers as somewhat futile, 
on the basis of the experimental facts they now have. More com¬ 
plete and more careful data from a variety of viewpoints are needed. 
The writers are convinced, however, that most of the difficulties in 
problems of salt absorption, water absorption, “ permeability, ” 
toxicity, and antagonism can be solved, and the mass of data concern¬ 
ing them unified by considering plant tissue as an amphoteric col¬ 
loid which reacts with ions according to chemical laws, rather than 
as a system of osmotic chambers with membranes of changeable 
permeability. 
SUMMARY 
When potato-tuber tissue was placed in small quantities of 0.001 
M. buffer mixtures of the potassium phosphates, and the reaction 
was determined electrometrically with the hydrogen bubbling 
continuously, solutions of P H 6.5 or greater became more acid, 
and solutions of P H 6.14 or less became more alkaline. Solutions 
of P ? 6.32 or 6.33 became more alkaline in some cases and more 
acid in others. 
In the majority of cases the equilibrium point reached with 
potato-tuber tissue under the conditions just referred to was P H 
6.37 to 6.46. The lowest equilibrium point reached from the alkaline 
side was P H 6.02, and the highest from the acid side was P H 6.44, 
When allowed to stand quietly fory>art of the time in larger quan¬ 
tities of the buffer mixtures, the final reaction reached, as determined 
electrometrically, was P H 6.3 to 6.86. 
When soy-bean root tips were placed in small quantities of 0.001 
M. buffer mixtures of the potassium phosphates, and the reaction 
was determined electrometrically with the hydrogen bubbling con¬ 
tinuously, solutions of P H 6.68 or greater were made more acid 
and solutions of P H 6.2 or less were made more alkaline. Solutions 
of P H 6.32 or 6.33 became more acid in some cases and more alkaline 
in others. 
61911-—25f-7 
