1915] LOEB—REGENERATION 261 
VI. Influence of root formation and of root pressure 
DEVRIES assumes with WAKKER that it is not the root forma- 
tion in itself by which the stem or main plant inhibits the growth 
in the notches of a leaf, but the root pressure. GOEBEL is inclined 
to think that it is the root formation in itself, regardless of the root 
pressure (or flow of water caused by it), which in- 
hibits the growth in the notches of the leaf. The 
writer has made a number of observations which 
indicate that of the two views that of WAKKER 
and DEVRIEs is better supported by the facts. 
As an illustration, we may take figs. 14 and 
15, in which a leaf with a piece of stem was 
suspended in moist air. The basal end of the 
stem formed a mass of roots, yet this did not 
prevent the growth of roots and shoots from the 
notches of the leaf. This contradicts GOEBEL’S 
assumption, but is in harmony with the view of 
DEVrIEs, since these roots in the air were not 
able to give rise to ‘‘root pressure.” 
As a further support, we may give the draw- 
ings (figs. 16 and 17). In these cases the leaves 
were cut off with only a fragment of the stem 
attached, which was a little larger in fig. 17 
than in fig. 16. The axillary bud was not 
removed. The leaves were suspended in moist 
air. Although the remnants of the stems formed 
roots, yet the leaves formed also roots and 
shoots (although they were in moist air). The 
root formation on the remnant of the stem pre- 
ceded the root formation on the leaf but did not 
prevent the latter. The experiment shows again Pi 46 bs 
that mere root formation in a stem suspended in 
moist air does not prevent the formation of roots and shoots in a 
leaf of Bryophyllum. It should be pointed out, however, that the 
shoots grew out from the axillary bud of the leaf; it is the growth of 
the opposite bud which has the inhibitory power on the leaf 
mentioned in the third and fourth sections. 
