532 Townsend ’ — Growth under Influence of Injuries. 
is severe, the acceleration will be preceded by a period of 
retardation of longer or shorter duration, depending upon the 
severity of the injury and upon the condition of the plant 
injured. 
The growth of the stems of older plants is accelerated by 
removal of a number of the roots or leaves, but is not affected 
by a slight injury to the roots. 
The roots of older plants as well as of seedlings are more 
independent than are the stems or shoots l . 
The change in the rate of growth of higher plants under the 
influence of a single irritation begins gradually, reaches its 
maximum in from twelve to ninety-six hours, and gradually 
diminishes until the normal rate is resumed. 
A dilute but continuous atmosphere of ether, or a strong 
shock of ether of short duration, will produce an acceleration 
in growth. 
The total variation in the growth of higher plants due to 
the influence of a single irritation is from o to 7o°/ o of the 
normal growth for the same period. 
The growth of sporangium-stalks of Phycomyces is suddenly 
and strongly retarded by cutting either the mycelia or another 
sporangium-stalk on the same plant. The growth does not 
entirely cease, and gradually recovers its normal rate in from 
thirty to sixty minutes. 
The influence of an irritation due to cutting or other injury 
is capable of acting through a distance of several hundred 
millimeters. 
1 Kny, l.c., p. 280. 
