198 GOEBEL: REGENERATION IN PLANTS 
activity by injuries, or they are outwardly invisible, there being 
simply a disposition or tendency toward the formation of new 
structures, as in adventitious buds, or adventitious roots. The 
two cases are not sharply distinguishable from each other, since 
in both the unfolding of a rudiment, or the awakening of a pre- 
disposition, is conditioned by the reciprocal connections of organs 
with one another, which are designated as “ correlations.”’ 
Fic I. Bryophyllum crenatum. Detached leaf, which has developed sprouts 
upon its edge, each with two small leaves. (In II made translucent so that the vena- 
tion is visible. } 
Some examples will make this point clearer. It is well known 
that every tree has hundreds of dormant buds which ordinarily do 
not awake, but which may be set into activity by cutting back, or 
by the destruction of the leaves during the vegetative season. 
My investigations were most closely concerned with the develop- 
ment of the buds which are normally present on the leaves of 
some Crassulaceae, as for example Bryophyllum crenatum, and 
which are laid down even in the embryonic condition of the 
leaves. Their presence implies that the leaves here serve the func- 
tion of reproduction, since every leaf that is cut off, if laid in 
damp earth, produces numerous young plants in the notches of its 
edges. 
The next question to be considered is by what means the devel- 
opment of the shoot-rudiments existing on the leaves is set in ac- 
