354 THE AMERICAN NATURALIST. [Vou. XXXII. 
The work follows along the lines of the author’s previous publica- 
tions relating to the pictographs of the American aborigines, and 
includes an account of these records and of the gesture signs in use 
among the Eskimos. The subject is treated comprehensively, with 
many comparisons to other culture groups. FR 
GENERAL BIOLOGY. 
Chemical Changes in Plant Stimulation.'— Hitherto we have 
had no test of the stimulation of a sensitive, responsive plant organ 
except the response itself. Czapek himself has been able to find in 
the terminal perceptive cells of the geotropically stimulated root no 
change in the protoplasm or cell sap, no visible movements in the 
mass, no secretory processes, no negative variation of the electric 
current such as the stimulated nerves of animals show, no change in 
osmotic cell pressure, no change in the normal, slightly acid, reaction. 
The new find is a chemical change in the protoplasm. When the 
root-tip of a seedling of a bean or other species is boiled in an 
ammoniacal silver nitrate solution, there is a marked reduction of the 
silver, especially in the cells of the periblem. This reduction is 
stronger in the célls of stimulated than in those of unstimulated 
root-tips. 
A second change consists in the diminution in the amount of a 
substance of the root-tip which easily loses oxygen. Such a sub- 
stance is indicated in the normal root-tip by such changes as these: 
blue coloration (oxidation) of a section of the root-tip by an emul- 
sion of guajac gum in water; deep blue coloration of sections by 
indigo white, made by careful reduction of indigo carmine by dilute 
hydrochloric acid and zinc; strong violet reaction (indophenol 
reaction) in sections subjected to an aqueous solution of a-napthol, 
to which paraphenylendiamin has been added. Now, all such reac- 
tions are less marked in the root after stimulation. Thus, stimulation 
results in increased capacity for reduction and diminished capacity 
for oxidation — an increased avidity for oxygen. 
These changes occur long before the response of turning shows 
itself, occur earlier the more sensitive the root, and are less marked 
after a slight stimulus such as results from a slight inclination of the 
root from verticality. 
1 Czapek, F. Ueber einen Befund an geotropisch gereizten Wurzeln. Ber., 
deut. bot. Ges., Bd. xv, pp. 516-520. January, 1898. 
