1915] LOEB—REGEN ERATION 263 
a flow of water in the stem and could not inhibit the growth of the 
shoots in the notches of the leaf; and by the time the leaf was 
put in water they were obviously not in a position to produce a flow 
or a root pressure. : 
' Roots formed on the stem have as a rule, therefore, an inhibiting 
effect on the growth from a leaf if they can produce a root pressure, 
that is, if they arein water. The formation of a shoot from the bud 
of a stem can produce such an inhibiting effect upon the opposite 
leaf if the shoot is in moist air and if no root is formed. This 
influence of roots on the growth of the notches of a leaf was dis- 
cussed only for the sake of completeness, since it does not strictly 
belong to our problem, which deals only with the growth of shoots. 
VII. The conditions inhibiting and accelerating the growth of 
the axillary buds 
Each node of Bryophyllum has one pair of leaves, and in the 
axilla of each leaf is found a bud which in the normal life never 
grows out, but which may grow out as a consequence of a mutilation 
of the plant. 
If we cut through two successive internodes of a stem and isolate 
a single node, and if we remove the two leaves, the two buds on the 
stem will grow out rapidly (if we provide the necessary water supply 
or if the node was cut out from near the base of the stem). 
If we remove only one instead of both leaves, only one bud will 
as a rule begin to grow, namely the one whose leaf is removed. 
This suggests the idea that the leaf, while favoring the growth of the 
opposite bud, inhibits the growth of its own axillary bud. If we 
remove neither of the two leaves, in many cases (especially in 
winter) neither bud will grow out, a fact which harmonizes with 
the assumption that each leaf suppresses the growth of its own 
axillary bud. 
The following experiment, however, restricts this last assump- 
tion that each leaf will inhibit the growth of its axillary bud. If 
we isolate a node with its two leaves (which we do not remove), 
and if we split the piece of stem longitudinally, we obtain two 
leaves, each attached to a half of a node containing the axillary bud 
of the leaf (fig. 20). In this case the axillary bud will grow out, 
