1905] McCCALLUM—REGENERATION IN PLANTS 261 
in a most fundamental manner the entire organization of the plant. 
All the meristematic tissue and in many cases much of the differ- 
entiated tissue contains various potentialities of growth, potentialities 
which seem impossible of expression while in organic connection 
with certain growing parts. This interdependence of parts may be 
manifested in an inhibiting influence, as in the case of the roots or 
shoots mentioned, or in an accelerating effect, as in the growth of 
the fruit and adjoining parts after fertilization, or perhaps more 
correctly with the developing of the embryo. The experiments 
described indicate that the means of accomplishing this, that is the 
means by which, for example, a terminal bud suppresses the develop- 
ment of the other growing points on the stem or leaf, do not lie in 
the withdrawal by the former of the nutritive materials or the 
water. The theory of specific formative materials fails to account 
for it; nor does the tension hypothesis add anything to our knowl- 
edge of the process. Correlation, the endeavor of the plant to 
teplace something lacking (DrrescH), and form-stimulus (Kor per- 
jormreizen of NOLL) are statements of the phenomenon and not at 
all explanations. 
Protoplasmic stimuli emanating from various parts, reaching 
often throughout the entire organism, and affecting the behavior of 
the protoplasm of even remote portions are quite conceivable; so 
also are the formation and diffusion of ferments controlling growth; 
but we have yet no evidence of the existence of either. | 
SUMMARY. 
A brief summary of the general conclusions thus far may be 
made as follows: The occurrence of regeneration in plants usually 
involves the replacement of parts removed, but the same result is 
often obtained when the organ is not removed, but is prevented from 
functioning, It is often inseparable from the ordinary growth of the 
plant, as for example when buds arise on the leaves of Tolmiea or 
Mine in ordinary course of the vegetative development of these 
Sag and the causes here are, no doubt, not different from those 
t induce the origin of buds on the growing points of the stem. 
Plant possesses innumerable growing points either organized or 
Potential, the vast majority of which must not be allowed to develop 
