260 BOTANICAL GAZETTE [OCTOBER 
‘DeVries describes a very striking experiment which supports 
the idea of WAKKER that the root of the main plant is the factor 
which inhibits the growth of the notches in the normal plant. 
The apices of six plants were cut off beneath the most vigorous adult leaf 
and planted in soil. After strong roots had been formed (in the soil) their 
stems were cut above the lowest pair of leaves, the apices removed, and this 
lowest pair selected for the experiment. Both leaves were put flatly on moist 
sand, the one after having been removed from the stem, while the other remained 
connected with the roots. The axillary buds were destroyed. After three 
weeks the isolated leaves had formed numerous young plants on their margin. 
The leaves which had remained connected with the rooted piece of stem had 
formed no plants in their notches (and did not form any afterward), although 
they had otherwise been exposed to the same conditions as the isolated leaves. 
This experiment is in harmony with the view that the normal 
roots of a stem (if they are under normal conditions) inhibit the 
growth of notches in the leaves. D£EVrIEs reports a second experl- 
ment in favor of the view of WAKKER. He cut the stem of a plant 
in its internodes and thus isolated seven pairs of leaves. 
From each pair one leaf was broken off; all axillary buds were destroyed. 
The leaves were now put on moist sand. After a month the seven stems had 
formed roots. The isolated leaves® had formed in their notches rooted plant- 
lets, varying from ro to 26 in number. The leaves whose stems had formed 
roots behaved differently. One leaf had formed no trace of growth in its 
notches; it was the one whose stem had formed roots first. The rest of the 
leaves had formed only a few plants whose number varied between 2 and 6 
They reached only a few mm. in length, while those of the isolated leaves 
measured from 0.5 to 2 cm. 
We see here that if a.root is formed on a stem before the roots 
in the notches of a leaf can grow out, the root (under proper con- 
ditions) may inhibit the growth of the notches of a leaf. 
While these facts leave no doubt that the root (under proper 
conditions) can inhibit the growth of the notches in the leaves of 
Bryophyllum, the experiments mentioned on the previous pages 
of this paper show that this is not the only factor. A piece of stem, 
even if it does not form any roots but only a shoot, will inhibit 
or greatly delay the growth of the notches of a leaf connected 
with it. | 
° That is, those broken off from the stem. 
