540 Blackman and Matt had, — On the Reaction of 
siderable distance. This indicates again a departure from 
the usual type of reaction, a special effort — so to speak — 
made to secure the exfoliation of all these extensive dead 
masses. 
It is difficult to resist the conclusion that the leaf is reacting 
as an autonomous whole and modifying the usual parallel 
absciss-line, to suit the special difficulties of its condition. 
The behaviour of this leaf seems to us to strongly support the 
view, suggested by the great vitality of these isolated leaves, 
that the solidarity and autonomy of a single leaf may be 
considerable. 
II. 
All the leaves described above were kept moist in beakers, 
as has been stated. When leaves attached to the shrub 
growing in the open were experimented upon, the reaction 
to incisions was found to 
be quite different, and it 
never took the form of 
the exfoliation which we 
have just described. 
If cuts be made with a 
scalpel through the leaves 
of Cherry-Laurel, while 
still on the plant, they 
quickly become bordered 
with a very narrow edge 
of dry brown cells, and in a week or two a translucent line 
may form parallel and very close to the brown edge of the 
cut. This is an occlusion-line of normal structure, and a line 
of active cell-division forms in it on the side towards the cut 
edge. No trace of separation is found , however, between the 
daughter-cells that arise from it, but they remain compactly 
adherent and division is continued, so that a periderm of 
several layers of cork results, as is shown in Fig. 8. 
Let us now turn to the records of previous workers, before 
we consider the problems that these reactions suggest. There 
Fig. 8. 
