92 BOTANICAL GAZETTE [AUGUST 
rather than, as often assumed, from the transportation of specific 
chemical substances. In other words, physiological correlation 
is fundamentally transmissive rather than transportative in char- 
acter, and transportative correlation arises only secondarily as the 
result of the quantitative and qualitative differences associated with 
the transmitted changes. It is evident that the existence of orderly 
transportative correlation demands the existence of differences of 
some sort arranged in an orderly way, and it is this fundamental 
order from which the other orderly phenomena in the life of the 
organism result, that this theory of the individual attempts to 
account for. 
It is not necessary to assume, however, that every individual 
arises in the manner described above. When an axial gradient 
is once established in a cell or cell mass, it may persist through 
division or other forms of reproduction, so that each axis of the 
offspring is simply the axis of the parent or a fraction of it. In 
such cases the processes of rejuvenescence associated with repro- 
duction bring the different fractions to essentially the same physio- 
logical condition, that is, the fraction which represents the lower 
levels of the parent gradient is brought up to the same metabolic 
rate or rates as that representing the higher levels. Nevertheless, 
we must, I believe, go back to a differential action of factors external 
to the protoplasm concerned for the origin of the metabolic gradient 
and so of the axis or polarity of which it is the simplest form. 
Since the energy or effectiveness of a transmitted change in 
protoplasm decreases with increasing distance from the point of 
origin, the length of,a metabolic gradient, and therefore the range 
of dominance of the region of highest rate, is limited, the limit 
varying with rate or intensity of metabolic activity, irritability 
and conductivity of the protoplasm, etc. This limit represents the 
maximum size which the physiological individual can attain and 
remain entirely an individual under the conditions which determine 
the limit. If, in consequence of continued growth, of decrease in the 
metabolic activity of the dominant apical region, of decrease in 
the conductivity of the protoplasm, any part previously within 
the range of dominance, that is, within the limit of length of the 
metabolic gradient, comes to lie beyond this limit, it becomes 
