( 138 ) 
successively leaflets A, B, C, Dand &. In a similar way 
in Trzfolium pratense (f. 3) we may call the three leaflets, 
AX, Yand Z. 
The removed leaflet in all cases is the one at the immediate 
right of the terminal one. This is leaflet Din Partheno- 
cissus and Lupinus and leaflet Z in Trzfolium. In f. 2 
and 3 the removed leaflet is represented by a barred line. 
The operation was performed as soon as the leaves started to 
unfold. The excision was made with a pair of dissecting 
scissors as near the base of the leaflet as was possible without 
injuring the other members. The cut surface was small, 
there was little or no exudation of sap and the wound healed 
inashorttime. A slight scar remained and persisted through- 
out the experiment, serving as an unfailing mark for the de- 
termination of the identity of the remaining leaflets. 
The Period of Growth. — After the removal of the leaflet 
in the operated series, both normal and operated groups were 
allowed to grow under conditions as nearly alike as possible. 
The period of growth was extended until the leaves had at- 
tained their maximum size and the experiment was closed 
only when there began to be danger of error on account of 
the drying up of some of the leaflets. The length of time 
varied in the different species, but in any one of them all the 
specimens, of both the normal and the operated series, were 
measured on the same day, so that the results show no error 
due to a difference in age. In Parthenocissus the length of 
the period of growth was thirty days, in 7rz/folium twenty-one 
days and in Lupinus forty-one days. 
The conditions of light, heat and moisture were kept as 
nearly alike as possible in the two series. In Parthenocrssus 
the position of the vines on a wire gave the different leaves 
very similar intensities of light. The plants of Lupénas and 
Trifolium were put in flower-pots kept at some distance apart 
in order to avoid shading. 
The Method of Taking Measurements.—In each of the 
species, when the leaves had attained their maximum size all 
