PHYSIOLOGY: J. WEB 
121 
Summary. — By measuring the influence of the mass of a leaf attached to an 
isolated piece of stem upon the process of regeneration in the piece, it has been 
possible to prove that the quantity of regeneration is in equal time and under 
equal conditions in direct proportion to the mass of the leaf. Since nothing 
except substances produced and sent out by the leaf can vary in direct propor- 
tion to its mass, it follows that the quantity of regeneration in an isolated 
piece of an organism is under equal conditions determined by the mass of mate- 
rial necessary for growth circulating in the sap (or blood) of the piece. If we 
measure the rate of regeneration by the mass of material regenerated in a 
given time, the law of regeneration becomes a special case of the law of chemi- 
cal mass action. That this mass action on a bud is only possible in a piece of 
stem after it is isolated, the writer explains on the assumption that the apex of 
an intact plant sends constantly inhibitory substances into the stem prevent- 
ing the buds contained in the stem from growing and consuming the material 
required for growth. When a piece of stem is isolated, the supply of these 
inhibitory substances from the growing region ceases and the most apical bud 
being the first to become free from the inhibitory substance will then come 
under the influence of the acting masses of the substances in the sap and regen- 
eration will occur. The mystifying phenomenon of an isolated piece restoring 
its lost organs thus turns out to be the result of two plain chemical factors: 
the law of mass action and the production and giving off of inhibitory sub- 
stances in the growing regions of the organism. 
^oeb, J., Science, New York, 45, 1917, (436); Bot. Gaz., Chicago, 65, 1918, (150). 
2 Loeb, J., Science, New York, 46, 1917, (547). 
