Apr., 1923 ] 
ADDOMS — HYDROGEN ION AND PROTOPLASM 
213 
ated with high concentrations of potassium di-hydrogen phosphate and 
consequent high hydrogen-ion concentration. Excessive branching of 
roots and stimulation of the growth of root hairs have been observed by 
Hoagland (’17), although he does not mention the characteristic stubbiness. 
This injury to the roots, which antedates injury to the tops, conceiv¬ 
ably and apparently renders the roots unable adequately to perform their 
functions, and presumably thus causes the later decreased growth of tops 
observed by other writers. Since the substances in the nutrient solution, 
as they pass into the plant, encounter the root hairs first, the effect upon the 
protoplasm of these cells was investigated, and the problem was accordingly 
narrowed at this point in the investigation to the changes that take place 
in root hairs. 
Protoplasm consists, at least chiefly, of substances in the colloidal state. 
This has been known ever since the dark-field microscope came into use 
among biologists, although the precise nature of the colloids is as yet un¬ 
determined. Gaidukov (To) described protoplasm as a sol because he 
observed many characteristics—for example, Brownian movement—that 
suggested a liquid condition. Since this pioneer work was published, 
however, studies of a greater variety of cells, and of the same cell under 
different external conditions, have shown that protoplasm is not to be so 
briefly characterized. Seifriz (’20) disagrees with Kite (’13) in his belief 
that protoplasm is ever so rigid that it can be cut into pieces that do not 
change in shape, and states that its cohesion is never greater than that of a 
plastic and viscous jelly. He found by micro-dissection that the streaming 
protoplasm of Rhizopus is fluid, while the endoplasm of Amoeba is decidedly 
viscous. After experimenting with protoplasm from many kinds of cells, 
both plant and animal, he concludes that within a given cell the viscosity 
decreases as the protoplasm becomes more active, and increases as it be¬ 
comes more quiescent. This phenomenon had already been observed by 
Price (T4), who noted that the protoplasm of Mucor spores changes from 
jelly to sol as the spores germinate, and that the protoplasm of Fucus eggs 
changes from sol to jelly as the eggs mature. The general conclusion to 
which the work of these and other investigators points is that the viscosity 
of protoplasm is not constant; it is different in different cells, it may be 
different in the same cell at different times, and, indeed, it is highly proba¬ 
ble that it is different in different parts of the same cell at the same time. 
Chemically, protoplasm probably consists of a “complex of substances 
of various chemical natures and in various states of aggregation, associated 
by forces of surface tension, electrical charge, and so forth.” 3 The exact 
nature of this complex is as yet undetermined; Lepeschkin (T3) believes 
it to consist largely of proteins and lipoids, while MacDougal and Spoehr’s 
(’20) “bio-colloids,” which simulate in many ways the colloidal behavior of 
protoplasm, are mixtures of proteins and pentosans, and are greatly in- 
3 Bayliss (T8), p. 26. 
