June, 1921] 
CHILD — PHYSIOLOGICAL CORRELATION 
291 
The relation of dominance and subordination does not necessarily 
persist in its primitive form throughout life. In animals, for example, the 
development of the nervous system, with highly specialized paths capable 
of transmitting excitation so much greater distances than embryonic proto- 
plasm, makes possible a much more complete and extensive dominance, 
which nevertheless is built up on the basis of the primitive relation. On the 
other hand, the qualitative differentiation of different organs affords a 
basis for complex chemical or transportative correlation. In plants, buds 
which are inhibited for a time may sooner or later become incapable of 
development, even when physiologically isolated, either because they have 
not been able to develop channels for the passage to them of water and 
nutrition, or because of changes in the cells in consequence of the action of 
the dominant region upon them. On the other hand, even in plants the 
conductivity of certain tissues may increase with differentiation and domi- 
nance be possible over greater distances than at first. In short, the primitive 
transmissive relation may develop and attain greater importance in certain 
types of relation, or it may be supplemented or even replaced by chemical 
correlation, or, finally, with advance in differentiation of parts the correlative 
factors may be chiefly nutritive. In any case the situation in the plant 
remains much simpler than in the higher animals, in which both the trans- 
missive and the transportative relations are extremely complex. 
My work on plants, in which Dr. A. W. Bellamy assisted me, was under- 
taken with the hope of being able to throw some light on the question of 
the nature of dominance and subordination as it exists in the growing plant. 
Thus far I have merely succeeded in blocking by means of low temperature 
the correlative factor on its way without interfering to any marked degree 
with the flow of fluids in the plant. As I have pointed out elsewhere, the 
results favor the view that correlation is accomplished by a transmission 
rather than by mass transportation of special substances, but much remains 
to be done before positive conclusions are permissible. 
My experiments thus far have been chiefly with three plants, Bryophyllum 
calycinum, Phaseolus multiflorus, and Saxifraga sarmentosa. The method of 
experiment and the results obtained with Bryophyllum have already 
appeared in the Botanical Gazette. As regards method, it may be said here 
that the low temperature is applied by surrounding the zone to be cooled 
with a coil or loop of small block-tin piping which can readily be bent and 
adjusted and through which water of controlled temperature flows. The 
region to be cooled is first wrapped in tinfoil and direct contact with the 
piping is avoided, the space between the coil and the plant being loosely 
packed with slightly moistened absorbent cotton, and the whole region of 
the plant and the coil after adjustment well wrapped in order to reduce 
temperature change from external sources to a minimum. All cases in 
which visible external injury due to pressure or to too low temperature 
occurs are discarded. Temperatures ranging from 3° to 8° C. are used 
