1918] LOEB—CORRELATION 163 
approximately the same weight of shoots per gram of leaf in the same 
length of time. 
When a leaf is isolated and put on moist filter paper or if it is 
suspended in moist air, as a rule more than one notch grows out 
into a shoot (fig. 6). This seems to indicate that the material 
available for shoot formation in one leaf does not all flow easily into 
one notch, so that we should expect that the material available in a 
leaf might be utilized more completely if the leaf were cut into 
several smaller pieces than if all the material had to go into one 
shoot only. This fact is evident from the following experiment. 
In one leaf the whole edge (containing the notches) with the 
exception of one notch was removed (fig. 9). Such a leaf could 
form only one shoot. The sister leaf was cut into 4 pieces but the 
edges were left intact. These 4 pieces could form at least 4 shoots. 
Fig. 9 shows such a pair of sister leaves. It was to be expected that 
the total weight of the shoots formed by the 4 pieces would be 
approximately equal to that of the one shoot in the sister leaf, or 
exceed it slightly for the reason indicated. Table IX shows that 
6 shoots produced in 6 whole leaves differed very little in weight 
from the 32 shoots produced by their 6 sister leaves, each of which 
was cut into 4 pieces, but that the difference was in favor of the 
leaves cut into 4 pieces. .The latter produced per gram leaf 93 mgm. 
of shoots, the former 84 mgm. Ina second set of experiments the 
difference was in the same direction, but a little larger, namely 
98 mgm. and 74.5 mgm. (table IX). While these experiments con- 
firm the law of equal production of shoots by equal masses of leaf, 
they also indicate that several shoots can consume the material 
available in one leaf more quickly than if only one shoot is present. 
A second complication is encountered when small pieces con- 
taining one notch are cut out from a leaf (fig. 6). In this case it 
may happen that when the piece is too small the notch of the small 
piece may not form any shoot at all, or the growth may be materially 
delayed. This is intelligible on the assumption that if the quantity 
of material available falls below a certain minimum no shoot can 
grow out. Fig. ro illustrates this statement. A large and a small 
piece were cut out from the same leaf, each piece containing one . 
notch only, the notches in each set of two pieces originally being 
