216 
AMERICAN JOURNAL OF BOTANY 
[Vol. io, 
Hairs from plants grown in solutions 2 and 3, of which the hydrogen-ion 
concentration is higher (pH 3.85 and 3.68 respectively), contain more vacu¬ 
oles, but there is no indication of coagulation. Decided differences are 
apparent between the protoplasm of root hairs grown in solutions 4 and 5, 
which are still more acid (pH 3.60 and 3.47 respectively), and that of the 
root hairs mentioned above. Hairs from solution 4 show the beginning of 
gel-formation: a coagulum has begun to form, the dispersion has decreased 
sufficiently to enable one to distinguish individual particles, and these are 
becoming flocculated into larger masses; however, there are still large 
portions of the protoplast that do not show coagulation. In hairs from 
solution 5, gel-formation is more pronounced: coagulation and flocculation 
are evident throughout the protoplast. In some places the flocculent 
masses are collected in the interior of the cell, thus indicating that the root 
hair is not turgid and is consequently of no value as an absorbing organ. 
Some protoplasm is still unprecipitated, but the amount is so small that 
it is almost imperceptible because of the contrast between the dark back¬ 
ground and the white, flocculent masses of irreversible gel. 
As has been noted above, this gel-formation occurs in the root hairs 
taken from cultures that have a large phosphate content, and consequently 
a large hydrogen-ion content, and it does not occur in root hairs grown in 
solutions containing a smaller proportion of the phosphate. Since the 
calcium-magnesium ratio is the same in all these solutions (except solution 
3, which, although it differs slightly in calcium-magnesium ratio, was in¬ 
cluded in the present experiments because it is generally considered Shive’s 
“ best” solution), and since there is no evidence to show toxicity on the part 
of any of the other ions in these solutions, the conclusion that the gel-for¬ 
mation is due to the hydrogen ion seems inescapable. 
This correlation is further supported by experiments that were performed 
to determine the effect of acids on protoplasm. In these experiments the 
hydrogen-ion concentration was varied, not by changing the salt proportions 
in nutrient solutions, but by irrigating the root hairs with solutions of an 
inorganic acid in pure water. The seeds were germinated on porous pottery 
kept moist with tap water, and the plants were taken directly from the 
pottery germinators for study when they were two or three days old. In 
this drier habitat they produced an abundance of root hairs. Moreover, 
the protoplasm in these root hairs was apparently denser, for under the 
dark-field microscope they appeared whiter. The osmotic pressure of the 
root hairs was also increased, for they were not plasmolyzed by a 0.45 M 
solution of hydrochloric acid, sodium chloride, or nitric acid. 
A gel is a solid formed from a sol or a jelly by the action of heat or of chemical reagents, 
i.e.j by processes other than mere loss of water. It is irreversible because the sol or jelly 
state cannot be regained by addition of water. 
Precipitation or coagulation is the formation of a gel. It may be accompanied with a 
decrease or an increase in the dispersion of the particles. 
Flocculation is the aggregation of precipitated particles into large, soft masses that 
remain suspended in the medium. 
