1915] LOEB—REGEN ERATION 269 
experiment, which has often been repeated, succeeds easily if the 
piece of leaf left around each notch is not too small. It is noticeable 
that the rapidity of growth is greater in shoots which grow out 
from a whole leaf than in those growing out from the isolated 
notches. Here we see again an application of the rule that if an 
organ a inhibits the growth in 0, the presence of b accelerates the 
growth in a. This is intelligible on the assumption that the leaf 
furnishes a flow of liquid containing material for the growthof shoots; 
and that the flow of 
this material away from 
the notches (wherever 
this may be) leads to 
‘the inhibition of the 
leaf around an isolated 
notch is too small, no 
growth may occur or 
only tiny roots or shoots 
will grow out. This 
observation again agrees 
with the assumption 
that a notch of a leaf 
will grow into roots and 
shoots if certain sub- 
stances or formed con- 
stituents of the leaf flow b 
toward a notch or are 33 
prevented from flowing Fics. 33 AND 34 
away. 
We can understand the experiment illustrated in fig. 37 on the 
assumption that if in a leaf one or more notches begin to grow out 
into roots and shoots, these shoots determine a flow in the rest of 
the leaf in a similar way as if a piece of the stem had remained 
attached to the leaf; and with the same inhibitory or retarding 
effect upon the growth of the other notches of the leaf. If, how- 
ever, each notch is isolated and given enough water (for example, if 
