1916] CHILD—GRADIENTS IN ALGAE 113 
Summary 
1. In 14 species of marine algae, including 10 species of Rhodo- 
phyceae, 2 of Phaeophyceae, 1 of Chlorophyceae, and 1 of Cyano- 
phyceae, a more or less definite gradient in susceptibility to KCN 
exists in the vegetative axes, and in several species in other parts 
also; the susceptibility being greatest, at least during growth and 
development, in the apical region and decreasing basipetally. 
2. Since extended experiment with the lower animals indicates 
that the degree of susceptibility to cyanides and to many other 
agents and conditions is in a general way, and within certain limits, 
a rough measure of metabolic activity or of certain fundamental 
metabolic processes, probably primarily the oxidations, these axial 
differences in susceptibility in the algae are regarded as indicating 
the existence of axial metabolic gradients. If this conclusion be 
correct, the axis in these simple plants is identical with the axis of 
the animal organism in this respect. 
3. The relations of physiological dominance and subordination, 
of physiological isolation and of differentiation to metabolic 
gradients, are briefly considered. 
Hvutit ZooiocicaL LABORATORY 
UNIVERSITY OF CHICAGO 
LITERATURE CITED 
1. Cuizp, C. M., Studies on the dynamics of morphogenesis and inheritance 
in experimental reproduction. II. Physiological dominance of anterior 
over posterior regions in the — of Planaria dorotocephala. Jour. 
Exper. Zool. 11:187-220. figs. 2I. 1911. 
ibid. III. The ica of new zooids in Planaria and other 
forms. "Jour. Exper. Zool. 11: 221-280. figs. 36. 1916. 
, ibid. IV. Certain dynamic factors in the regulation of Planaria 
dorotocephala in relation to the axial gradient. Jour. Exper. Zool. 13: 103- 
152. figs. 46. 1912. 
4.-——, ibid. V. The relation between resistance to depressing agents 
and rate of reaction in Planaria dorotocephala and its value as a method of 
investigation. Jour. Exper. Zool. 14:1 53-206. jigs. 2. 191 
, ibid. VI. The nature of the axial gradients in Planaria and their 
relation to antero-posterior dominance, polarity, and symmetry. Arch. 
f. Entwickelungsmech. 37: 108-158. figs. 13. 1913. 
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