1916] CHILD—GRADIENTS IN ALGAE 10g 
susceptibility gradient exists. To these may be appended some 
fragmentary observations on the blue-green alga Calothrix, which 
indicate that even in this simple form a basipetal susceptibility 
gradient exists. Although the observations are incomplete at 
many points and further work on other stages and species is neces- 
sary, the uniformity of results is striking and cannot but suggest 
that the order observable along these axes and the susceptibility 
gradients are in some way associated. If the susceptibility method 
is of any value as an indicator of general metabolic or oxidative 
activity, the susceptibility gradient represents a gradient in meta- 
bolic or oxidative activity, the most susceptible regions being the 
most active. If this be true, the axes of these simple plants possess 
primarily the same metabolic characteristics as the axes of animals 
in this respect. Such a fundamental resemblance or rather identity 
as this must possess some fundamental significance, and. in the 
introductory section of this paper my views concerning this sig- 
nificance are briefly stated. Many lines of evidence have forced 
me to the conclusion that this axial metabolic gradient is the basis, 
the starting point of the order in space and time which is character- 
istic of the axes of organisms. In short, according to this point 
of view, the axis, whatever else it may become during development, 
is fundamentally a metabolic gradient. The order along the axis 
is primarily an expression of this gradient. The organic or physio- 
logical individual, as distinguished from other kinds of individuality 
which may exist in the organism and in the inorganic world, con- 
‘sists fundamentally of one or more metabolic gradients. The 
various aspects of this conception of the organic individual and their 
bearing on biological problems have been considered elsewhere 
(12), and it is impossible here to do more than note the complete 
agreement with the general conception of these observations on 
plants. 
From this point of view there is a fundamental identity in the 
apical regions of plant and animal organisms and in their relations 
to other parts. I have suggested elsewhere (12, pp. 189-192) that 
the fact that the apical region of the animal gives rise to the highly 
specialized and physiologically stable cephalic nervous system or 
brain, while that of the plant remains indefinitely or for a long time 
