(135) 
ration more or less definite for each species. As a further 
consequence each member must respond not as a unit but 
as part of a system. If now we have a system of this 
kind with a definite configuration due to the mutual interac- 
tion of its members and we remove one of the component 
parts, we must get a disturbance of the equilibrium leading 
to changes in the relations of the remaining parts limited only 
by the extent to which the rigidity of the skeletal structures 
may counteract such a tendency. We may in this manner 
get at the forces which are active in correlation at the time of, 
and subsequent to, the operation. The main difficulty with 
the method must consist in the reaction to the stimulus of the 
injury itself, a factor which does not enter into the normal 
relations of the parts. 
The special method chosen for these experiments aimed to 
carry along two parallel series of leaves, one with the normal 
relations of its members undisturbed and the other with a par- 
ticular leaflet removed at the earliest possible stage. When 
the leaves had attained their maximum size, measurements of 
the length and of the angular position of the leaflets were 
taken. A comparison of the two series of figures gives the 
change produced as a result of the removal of the leaflet, be- 
cause, according to the conditions of the experiment, all the 
other factors are alike. It is evident that the success of the 
method depends largely upon the care exercised in keeping 
the conditions of the two series the same. With this in view 
special precautions were taken in the choice of the leaves, in 
the obtaining of similar environments during the period of 
growth, and finally in the choice of the method of meas- 
urement. 
THe MeEruHop. 
The method may be conveniently described under five 
heads : 
1. The choice of leaves. 
2. The operation, 7. ¢., the removal of one of the leaflets 
in each leaf of one series. 
3. The period of growth. 
