under the Influence of Injuries . 529 
entire length of the root in order to affect the growth of 
the shoot. This distance, as shown by the tables, varied 
from twenty to fifty millimeters. In like manner, when the 
shoot was injured, it was necessary for the influence of the 
irritation to travel nearly the entire length of the root in 
order to affect the growing-zone. Furthermore it was not 
sufficient for the irritation simply to reach the growing-zone, 
but it was necessary for it to extend through a part or all of 
the cells of the zone in order to affect the growth. 
In the older plants the distance through which the irritation 
acted was much greater than in the seedlings. In Phaseolus , 
for example, the entire growth of the stem, after the roots 
were injured, took place above the first pair of leaves, which 
were from 95 to 150 mm. above the root. The secondary 
roots were injured at least 20 mm. from the main root, so that 
the distance from the point of injury to the growing-zone of 
the stem was from 115 to 170 mm. In the Phaseolus plants 
in which the roots extended into damp chambers before 
injury, the distance was still greater. The flower-pots used 
were no mm. deep. This added to the 95 or 150 mm. made 
a distance of from 205 to 260 mm. through which the influence 
must have acted. In Calla the distance between the point of 
injury and the zone of growth varied from 50 to 80 mm. In 
Phycomyces the distance was from 10 to 50 mm. 
These distances are by no means to be regarded as the 
limits through which such irritation will influence growth. 
The distance through which an influence will act depends 
upon the degree of injury and upon the external and internal 
conditions of the individual plants. 
Time . — In experiments relative to the time required for the 
influence of the irritation to exhibit itself, observation with 
the horizontal microscope showed that there was no sudden 
change, due to injury, in the rate of growth of higher plants. 
It was only by extending the period of observation over 
several hours that a distinct difference in the rate of growth 
could be detected. It is therefore impossible to say definitely 
at what time an acceleration or a retardation of growth began. 
