THE EFFECT OF THE HYDROGEN ION ON THE PROTO¬ 
PLASM OF THE ROOT HAIRS OF WHEAT 
Ruth M. Addoms 
(Received for publication September 6, 1922) 
In modern experiments with nutrient solutions in which phosphates are 
provided as either potassium mono-hydrogen or potassium di-hydrogen 
phosphate, it has been found by several writers that in fairly high concen¬ 
trations these phosphates are injurious. Hoagland (’17), Duggar (’20), 
and Salter and Mcllvaine (’20), indeed, found that if the concentration of 
phosphate was increased to but a slight extent, its injurious effect was 
marked. Since phosphorus is essential for the growth of plants, and is 
actually a constituent of protoplasm, it is not at once clear why its influence 
should so suddenly change from beneficial to harmful as its concentration 
is increased in the culture solution. The unquestioned nutritive value of 
the phosphate ion and of the potassium ion directs attention to the other 
component of the salt, the hydrogen ion. A logical first step in determining 
the nature of the harmful effect might be to ascertain by inspection whether 
it is general or local; to see if any particular cells behave or develop differ¬ 
ently in solutions containing a large amount of phosphate than in solutions 
in which the concentration is lower. 
For this purpose seedlings of spring wheat (Triticum vulgare), '‘Mar¬ 
quis” strain, were grown in solutions selected from Shive’s (T5) “optimal” 
group. The total osmotic pressure of each of these solutions was calculated 
by Shive to be about 1.75 atmospheres. Since the lime-magnesium ratio 
has been thought to influence the growth of plants, 1 solutions were chosen 
in which this ratio was practically constant. The compositions and hy¬ 
drogen-ion concentrations of the solutions employed are shown in table 1. 
The hydrogen-ion concentrations were determined colorimetrically with 
a colorimeter of the form described by Bock and Benedict (T8). The 
indicator used in these experiments was tetrabromphenolsulphonephthalein 
(brom-phenol blue), prepared according to the directions of Clark (’21). 
The buffer solutions used were mixtures of potassium hydrogen phthalate 
and hydrochloric acid, and of potassium hydrogen phthalate and sodium 
hydroxide (Clark, ’21); they were standardized by titration with dibrom- 
thymolsulphonephthalein (brom-thymol blue) against standardized hydro¬ 
chloric acid obtained from the LaMotte Chemical Products Company of 
Baltimore, Maryland. 
Baker’s “analyzed” chemicals were used for the culture solutions, 
which were made up from single-salt stock solutions drawn from covered 
1 For a general discussion see Lipman (’16). 
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