514 Townsend . — The Correlation of Groivth 
the growth of the higher plants, as well as of Phycomyces ; 
was measured by means of a horizontal microscope. 
Control-plants were used in all cases except with Phycomyces , 
and were selected according to their equality in size and 
rate of growth with those to be treated. 
Experiments. 
Seedlings . — Owing to the high degree of independence 
existing between roots and shoots, it was necessary to 
perform a large number of experiments in order to reach 
definite and satisfactory conclusions. No attempt will be 
made to give a detailed description of the individual experi- 
ments, but rather the general results obtained. In the 
following tables a series was made up from the averages of 
growth of a large number of seedlings for a definite period. 
In the second column P. indicates the period during which 
the injured and the uninjured plants were compared. The 
periods were often determined from a large number of ob- 
servations made at short intervals and combined ; e. g. if 
four observations were made at intervals of six hours, and 
each observation showed an acceleration of growth, the four 
observations were combined and given as one observation 
of twenty-four hours. All the numbers opposite a were made 
up from the averages of nine or more experiment-plants ; 
while the numbers opposite b were made up in the same 
manner from the same number of control-plants. The 
original length of roots and shoots indicates the length of 
these parts when measured for the determination of the 
normal rate of growth. The normal rate of growth was 
determined for all experiment as well as control-plants. The 
column headed ‘Average growth during first period after 
injury’ usually covered the time within which a change in 
rate of growth became apparent. The last column in each 
table is given for the purpose of showing how long the 
plants were under observation after treatment, and also for 
the purpose of comparing the growth of the injured and of the 
