1915] LOEB—REGENERATION 273 
grow out only if there is no flow of liquids (carrying non-formed 
or possibly formed material) away from the notches. This is not 
the case in the normal plant when the circulation is normal, and 
WAKKER and DeVries have shown the réle which the root pres-. 
sure plays in this case. But the root pressure is not the only factor 
which influences this flow. The experiments in figs. 1-3 seem to 
indicate that different factors aside from the root pressure can 
determine the flow away from the notches of the leaf, provided our 
assumption is correct that such a flow is the cause of the phe- 
nomena of growth and regeneration observed. 
If we go back to these first experiments in this paper and try to 
formulate them in harmony with this idea, we should have to state 
that in a completely isolated leaf the flow away from the notches 
ceases. As a consequence, one or more of the notches may grow 
out, and as soon as this happens the flow in the leaf is directed 
toward the growing notches. They act as if they exercised a 
“‘suction”’ on the flow of liquids in the leaf, and they may inhibit 
the growth in other notches of the leaf. 
If the leaf is in connection with a piece of stem, the latter exer- 
cises this “‘suction,’’ and the flow of liquids is away from the leaf 
to the stem; hence the inhibiting effect of the stem upon the growth 
of the notches of the leaf. This “‘suction effect” is especially great 
if the bud opposite this leaf can grow out, asin fig. 2. If both leaves 
are left attached to the piece of stem (as in fig. 3), the flow from a 
leaf will be deflected from the buds and may go into the opposite 
leaf. This might explain why when both leaves remain attached to 
a piece of stem the growth of the notches of the leaves is favored 
again, though it is not so rapid as in a completely isolated leaf. 
This idea of a deflection of the current away from the leaf 
toward the opposite side of the stem is in harmony with the fact 
that the bud opposite a leaf grows out very quickly if its own leaf 
is removed (fig. 2); while the growth of the axillary bud of the leaf 
which is not removed is inhibited in this case. If we split the stem 
longitudinally, this deflection ceases and the leaf ceases to inhibit 
the growth of its own axillary bud. This idea is supported by the 
fact that if the leaf attached to a longitudinally split node is partly 
suspended in water its notches will grow out rather rapidly. 
