120 
PHYSIOLOGY: J. LOEB 
portional to the mass of growth material circulating in the sap (or blood) of 
the piece and required for the synthetical processes giving rise to the regen- 
erated tissues and organs. If we measure the rate of regeneration by the mass 
of material regenerated in a given time, the law expressed for the quantity 
holds also for the rate of regeneration and in this form the law becomes a special 
case of the law of chemical mass action. 
4. This law does not throw any light upon two other features of regenera- 
tion, namely, first, why it is that as a rule only the apical bud of an isolated 
piece of stem grows out and none of the buds situated more basally in the stem; 
and second, why it is that the same bud which grows out when the piece of 
stem is cut out from the whole plant does not grow out as long as the piece is 
part of a whole (and normal) plant. The writer published not long ago a 
series of experiments 2 which suggest that the growing apex (as well as the 
TABLE 3 
Influence of Mass of Leaves Upon Mass of Shoots Regenerated by Stem 
WEIGHT OF 
LEAVES 
WEIGHT OF 6 
REGENERATED 
SHOOTS ON 
STEM 
MILLIGRAMS OF 
SHOOTS RE- 
GENERATED 
PER GRAM OF 
LEAF 
grams 
grams 
Experiment I. Dura- ( 
6 whole leaves 
19.030 
2.808 
147 
6 sister leaves, reduced in size 
2.853 
0.443 
152 
Experiment II. Dura- ( 
6 whole leaves 
18,490 
3.586 
192 
6 sister leaves, reduced in size 
3.503 
0.668 
190 
leaves) of a plant continually produce and send toward the base of the plant 
substances which inhibit the growth of dormant buds. When a piece of stem 
is cut out from a plant these inhibitory substances contained in the stem will 
continue to flow toward the base, with the result that the most apical buds will 
be the first to become comparatively free from these inhibitory substances 
and hence will be the first to grow out. As soon as this happens, the growing 
buds will produce and send toward the base inhibitory substances, with the result 
that none of the more basally situated buds of the piece of stem can grow out. 
In the normal plant the material serviceable for growth can only be utilized 
by the growing region at the apex (and the base of the plant) ; and when a 
piece is cut out from the plant the same material becomes available for the 
growth of those buds which are the first to be freed from the inhibitory mate- 
rial which they contained while forming parts of the whole plant. The fur- 
ther qualitative as well as quantitative experiments which the writer has car- 
ried out since the publication of his preliminary note support this hypothesis. 
