118 
PHYSIOLOGY: J. WEB 
stem is cut out from a plant it will form shoots from its two most apical buds. 
My experiments have yielded the result that the mass of shoots formed in the 
latter case is in direct proportion to the mass of a leaf attached to the stem; 
and to the mass of the isolated leaf in the former case. The data concerning 
regeneration in an isolated leaf have already been published 1 but will be re- 
peated here to show the identity of the law in both cases. 
2. When we cut out two sister leaves of Bryophyllum . i.e., a pair of leaves 
taken from the same node of a plant, and keep them under the same condi- 
tion of moisture, temperature, and light, the two sister leaves possessing equal 
mass will produce approximately equal masses of shoots in equal times, although 
the number of shoots produced by the two sister leaves may vary considerably 
(table 1). 
TABLE 1 
Influence of Mass of Leaves Upon Mass of Shoots Regenerated by Leaf 
WEIGHT OF 
LEAVES 
NUMBER OF 
SHOOTS 
WEIGHT OF 
SHOOTS 
MILLIGRAMS OF 
SHOOTS PRO- 
DUCED PER 
GRAM OF 
LEAF 
grams 
grams 
Experiment I. Duration, 22 days. . / 
8 leaves 
8 sister leaves 
16.430 
16.476 
37 
40 
1.675 
1.682 
102 
102 
Experiment II. Duration, 29*days . . j 
9 leaves 
9 sister leaves 
12.022 
11.861 
24 
20 
1.436 
1.348 
119 
114 
f 
12 leaves, intact 
18.435 
25 
2.884 
156 
Experiment III. Duration, 30 days. . . j 
12 sister leaves, 
each cut into 4 
pieces 
17.070 
50 
2.747 
161 
When we reduce the mass of one set of the sister leaves (by cutting away 
parts of the leaf), while that of the other set remains intact, both sets of leaves 
will produce in equal time and under equal conditions shoots whose masses are 
approximately proportional to the masses of the two sets of leaves (table 2). 
From this it follows that equal masses of leaves produce equal masses of 
shoots, regardless of the number of shoots. Since chemical substances (water 
and solutes) are the only factors among those to be considered here which can 
vary in direct proportion with the mass of the leaves, it follows that the quan- 
tity of shoot formation in an isolated leaf is determined by the quantity of cer- 
tain material contained in the sap of the leaf. This material is probably 
the usual material required for growth: water, and certain solutes, sugar, 
amino acids, salts, etc. 
