1915] LOEB—REGENERATION 259 
end of the stem. Still later, roots and shoots began to grow out 
from the notches of the leaf (although this was not submersed in 
water). Fig. 14 was drawn January 18, therefore 9 weeks after 
the beginning of the experiment. About a week after the drawing 
was made, the stalk / which had wilted fell off and now the bud in © 
the axilla of the stalk / was able to grow and the shoot S was formed 
(fig. 14). The drawing (fig. 15) was made when the shoot was one 
week old. The experiment shows also incidentally that the root 
formation on the stem does not (under the conditions of this experi- 
ment) inhibit the formation of roots and shoots on the leaf. We 
shall return to this fact later. 
In this experiment the leaf was merely suspended in moist air 
and yet shoots developed from the leaf although it was attached to 
a piece of stem. This is unusual, since in order ‘to obtain such a 
result with certainty it is necessary to submerse part of the leaf in 
water. 
V. Inhibiting influence of roots on the growth of the 
notches of a leaf 
A piece of stem when cut from a whole plant of Bryophyllum 
is not only able to form shoots but it also forms roots, and it is now 
our intention to consider the influence which the root formation of 
the stem has on the growth of the notches of a leaf. WAKKER, 
DeEVries,?:and GOEBEL! all have reached the conclusion that it is 
the presence of the main root or the regenerated roots on the stem 
which prevent the growth of adventitious roots or shoots on the 
leaf. If we break or cut off a leaf of Bryophyllum calycinum from 
the stem, neither the stalk nor the base of the isolated leaf has 
the power of forming roots, and this inability of root formation is 
considered by WAKKER and DEVRIES to be the cause of the growth 
of the notches. ‘According to WAKKER the organic separation of 
the leaf from the rooted part of the plant acts as a stimulus upon 
the leaf and induces the growth in the notches.” 
3 DeVrirs, Huco, Jahrb. Wiss. Bot. 22:35. 1890. 
4GorBeL, K., Einfiihrung in die Morphologie der Pflanzen. Leipzig, 1908 
(pp. 142-149). 
’ DeVries, Huco, Joc. cit. The writer was not able to obtain WAKKER’Ss mono- 
graph, 
