250 BOTANICAL GAZETTE [OCTOBER 
correlation of growth. These rules are so simple and transparent 
that they form, in the opinion of the writer, a securer basis for 
hypothesis than is offered by most former experiments in this 
direction which have not led to such simple rules. 
-The advantage of this plant for the study of the problem of 
regeneration lies in the fact that shoots can grow out only from 
definitely located buds in the stem and in the notches of the leaf. 
The “Anlagen” of roots are not so definitely located, and roots 
may grow out apparently from practically any spot on the stem of 
the plant; they are, therefore, not so appropriate for the estab- 
lishment of definite and simple rules of inhibition, and their growth 
will not be considered in this paper. 
One bud is located in each notch of a leaf of Bryophyllum 
calycinum; when such a notch begins to grow it forms first roots 
and later shoots. It is well known that if the leaves of this plant 
are cut off and put on moist soil (or suspended in moist air) they 
will form roots and shoots from their notches. This is the mode 
of propagation of this plant. The question is: Why does a leaf 
not form roots and shoots in its notches so long as it is in connec- 
tion with a healthy plant? The buds in the notches of the leaf 
are not the only ones which are inhibited from growing when 
forming parts of the whole; the buds on the stem, one of which is 
found in the axilla of each of the two leaves in each node, are in 
the same condition, and the same question may be raised, namely: 
Why do not these buds grow out as long as they form part of a_ 
plant, while if isolated they may grow into shoots ? 
A very few words will suffice to show that the stimulus of the 
wound is not responsible for the growing out of buds, though the 
conditions at the edge of the wound are responsible for the healing 
or covering of the wound by the spreading of epithelial cells over 
the area laid free by the wound; and they may possibly be directly 
responsible for the callus formation in the case of plants. When 
we break off a leaf of Bryophyllum, the notches of the leaf will grow 
out into roots and shoots, but these notches are far away from the 
cut end of the stalk of the leaf. Moreover, as a rule, the notches in 
the middle of the leaf will grow out first, and not those nearest the 
wound caused by the cutting or breaking off of the leaf. It is 
