CHAPTER II 
THE PHYSIOLOGICAL BASIS OF AXIATE PATTERN 
THE PHYSIOLOGICAL GRADIENT 
The cell is primarily an organism, though it may be 
integrated with other cells to form a part of a multicel- 
lular organism. While we have no positive knowledge 
concerning the origin of cell pattern, the structure of 
the cell in general suggests that it is primarily what we 
may call a surface-interior pattern. If this is true, the 
differentiation of nucleus and cytoplasm from the primi- 
tive protoplasm, possessing in some degree the functions 
of both, must have resulted in the first instance from 
differences and relations between exterior and interior. 
Some organisms appear to be even simpler in pattern 
than the ordinary cell, but most of them are so minute 
and show so little differentiation of parts that our 
knowledge of their pattern is very fragmentary. Even 
in the simplest organisms, however, we should expect 
to find at least a surface-interior pattern. In the 
absence of any positive data, further discussion of the 
origin of cell pattern and of still simpler patterns is of 
value only in the light of what we can learn concerning 
other organismic patterns and is therefore postponed 
(see p. 60) . 
The surface-interior pattern is primarily a com- 
pletely radial, spherically symmetrical or centered 
pattern and, assuming that organismic pattern arises 
through relation between protoplasm and environment, 
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