r915] LOEB—REGEN ERATION 265 
this case the bud in the axilla of a leaf which is not removed will 
grow out rather rapidly. 
We may anticipate that all these experiments indicate that the 
growth of the bud depends upon the flow of certain substances 
from the leaf to the bud. That bud which receives these substances 
first will grow out first, and thereby prevent the flow to the other 
bud whose growth is thereby “inhibited.” The apparent inhibi- 
tion of growth in one place is simply due to the fact that under the 
conditions of the experiment the substances required for growth 
flow to some other place and are retained there, and the removal 
of the inhibition consists in creating conditions which will force 
the substances to flow where we want growth to occur. 
VIII. The rules and mechanism of inhibition in regeneration 
We cut off the base and tip of the main stem of a plant of Bryo- 
phyllum, remove all the leaves, and suspend the stem in a closed 
aquarium saturated with water vapor. Only the two buds at the 
highest apical node will grow out (fig. 23); it does not matter 
whether the stem is hung upright or inverted. The buds at the 
more basal nodes are all inhibited from growing by the growth of 
the two apical buds; for if we isolate any of the lower nodes, their 
buds also may grow (fig. 24). This is the well known example of an 
inhibition of ‘one part by another. In the terminology of REINKE, 
we might call the two apical buds the “dominants.” What is the 
source of their dominance? By way of an answer we intend to show 
that the following relation exists: If an element a inhibits the growth 
in an element b, b very often accelerates or makes possible the growth 
ina. Whenwe cut off a single node near the top of the main stem of 
Bryophyllum, remove the two leaves, and suspend it in an aquarium 
saturated with water vapor, as a rule the two buds will not grow out. 
If, however, we leave it in connection with one or more of the lower 
nodes of the stem, it will regenerate, and incidentally inhibit the 
growth in the lower nodes (figs. 23, 24). The regeneration and 
growth of the two shoots at the apical node will as a rule be the 
quicker the more nodes are left in contact with it. Hence the lower 
part of the stem whose regeneration is inhibited by the apical node, at 
