534 Blackman and Matthaei . — On the Reaction of 
removal of the roots may be followed by a second crop and 
even a third. Cherry-Laurel leaves, however, never produce 
roots, but they develop a callus from the cut surface of the 
leaf-stalk which forms a well-marked pad over it. 
Such recuperative processes indicate considerable vitality, 
but the remarkable activity of the leaf that can be induced by 
injury even after some weeks of starvation shows that the 
leaf is really in full vigour. 
We will confine ourselves in this paper to the case of the 
Cherry- Laurel {Primus Laurocerasus , garden var. rotundifolia ), 
and at first to its behaviour when the leaves used are such as 
have been cut off and are being kept in the laboratory in a 
beaker, with the cut stalks in water. A very loose lid is placed 
on the vessel so that the air surrounding the leaves is kept 
moist. If patches of cells of these leaves be killed — and this 
conveniently becomes evident by their turning brown very 
quickly — the surrounding sound tissues always react by cutting 
off and exfoliating the injured patch, so that it drops, without 
any external assistance right out of the leaf, and a hole 
results. The line of exfoliation follows the outline of the 
injury with some precision but at a certain distance from it, 
and so any number of holes of any desired outline can be 
brought about ; the leaves 2, 3, 5, 6, in Plate XXIX, are 
bizarre examples of the effect. 
The healing of wounded leaves has been previously de- 
scribed for several cases, but we can find no description of 
the . process of exfoliation which we have observed, and of 
which we may now give a detailed account. 
I. 
If a clean cut be made through the substance of a Cherry- 
Laurel leaf with a sharp knife no healing reaction follows. 
In ever so many cases ten or more incisions have been made 
in each half of the lamina, at right angles to the midrib and 
extending from the midrib right to the edge of the leaf. 
A leaf thus cut into some twenty segments, united only by 
means of the midrib, will if protected from too great dryness 
