170 BOTANICAL GAZETTE [FEBRUARY 
In both cases the water may play the réle of accelerating the velo- 
city of certain chemical processes which are needed for the formation 
of roots and shoots. 
The experiment just described never fails, and we may therefore 
say with some justification that in an isolated leaf suspended in 
1) moist air those notches will grow 
V/ out first which by chance have at 
first the necessary supply of water 
(or of sap in general). Those 
shoots which grow out first will 
then automatically inhibit the 
growth of the other notches by 
Ws drawing the solutes and the water 
toward themselves. 
2 This view is supported by 
| another set of experiments. In 
= — el the previous experiment the 
— ———— isolated leaves were first sus- 
=e te ———————— pended in moist air and after- 
7 TiS) ward allowed to dip into water. 
When we let the apex of the 
Fic. 15.—Leaf dipped with apex in iSOlated leaf dip from the begin- 
water; drawn after 28 days: in such ning into water, only those 
cases the shoot from one of watered notches will give rise to shoots 
piper pelea age a which are just under the level 
formation in notches in middle of leaf, Of the water or just above it 
where growth is most rapid, when leaf (fig. 15). Such shoots grow more 
ae og oe rapidly than the shoots of leaves 
suspended entirely in moist alr, 
and this fact also suggests that it is the quantity of water which 
decides which notches grow out first. It is also noticeable that . 
when an isolated leaf dips into water from the beginning the notches 
in the middle of the leaf, which would have given rise to roots 
(fig. 11) if the leaf had been suspended entirely in air, now generally 
fail to do so (fig. 15), if the leaf is not too large, presumably because 
the greater rate of growth of the notch dipping into water inhibits 
the growth of roots in the rest of the notches. With the greater 
