172 BOTANICAL GAZETTE [FEBRUARY 
many interlocking channels for the sap flow. It occurred to us 
that if we suspend such leaves in moist air with their longitudinal 
axes put horizontally (figs. 17, 18), the notches on the lower side of 
the leaf should form more shoots than the notches on the upper side, 
since the sap should collect in larger masses on the lower edge of the 
leaf. This is apparently the case, since very often shoots form only 
on the lower side of such a leaf, as in fig. 17 (where the notches in 
a, b, c had been removed before the experiment began). In fig. 18 
three notches formed on the lower and one on the upper side. The 
Fic. 17 Fic. 18 
Fics. 17, 18.—Leaves suspended in moist air with main axis in horizontal posi- 
tion: shows formation of shoots is favored on lower side, where water is bound to 
collect in larger masses; in fig. 17 notches at a, 6, c had been removed. 
experiment just mentioned and which has often been repeated 
supports the idea that the first shoots grow out where the water or 
sap collects, the water naturally having the tendency to flow 
downward. 
Light is an important factor in the shoot production of the leaf 
of Bryophyllum calycinum. Isolated leaves kept in the dark pro- 
duce a considerably smaller mass of shoots than their sister leaves 
kept in light, as the following experiment shows. Six leaves taken 
from different plants or nodes were suspended in the dark, either 
in moist air or were dipped with their apices in water; while their 
sister leaves were suspended in the same way but in light. Table. 
XII shows the difference in the amount of shoot production. 
