Leaves to Traumatic Stimulation . 541 
is no occasion for us to consider the literature of wound-heal- 
ing in general, as a good account was given of it by Massart 1 
a few years ago. Confining ourselves to leaves, we find that 
many different reactions have been observed on leaves in situ 
as a result of spontaneous, accidental or experimental injuries. 
Collating the chief papers, those by Bretfeld 2 , Frank 3 , and 
Massart x , we may distinguish at least five different cases, none 
of them involving formation of an absciss-layer. 
(1) In Camellia and in many marsh plants it is said that 
there is no reaction, and that the killed tissues dry up to form 
a scar over an injured surface 4 . 
(2) In Nuphar and other aquatic plants when the large 
internal spaces are laid open by injury there takes place a filling 
up of the lacunae by growth of the cells which border them 5 . 
(3) In Leucojum something similar takes place, but the 
outgrowing cells form long almost unseptate tubes, tightly 
packed and capable of uniting with the cells growing out from 
the opposite side of a cut, to make a union of the fracture. 
Frank considers this to be a primitive form of callus, and 
the cells, though thin-walled and of sparse contents, are cuticu- 
larized and resist sulphuric acid 6 . 
(4) In Cornus 7 and Hoya 8 we get septate outgrowths of the 
mesophyll-cells to form a compact mass of isodiametric cells 
without intercellular spaces, which Frank regards as a typical 
callus. 
(5) In succulent and in some other leaves several layers of 
corky cells may arise by division in the mesophyll-cells parallel 
to the surface of the wound. This takes place in quite the 
same way as the well-known new formation of cork below 
the wounded surface of a potato 9 . No increase in bulk of 
1 Massart, La cicatrisation chez les vegetaux. Mems. couronn^s de l’Acad. roy. 
de Belgique, T. 57, 1898. 
3 Bretfeld, Vernarbung u. Blattfall, Pringsheim’s Jahrb., vol. xii, 1879. 
3 Frank, Die Krankheiten der Pflanzen, Breslau, 1895, Bd. i; cf. also the section 
on the same subject in Schenk, Handbuch der Botanik, Bd. i. 
4 Bretfeld, loc. cit., p. 139. 5 Massart, loc. cit, p. 41, Fig. 43. 
6 Frank, loc. cit., p. 65, Fig. 12. , 7 Frank, loc. cit., p. 67, Fig, 13. 
8 Massart, loc. cit., p. 57, Fig. 54. 9 Bretfeld, loc. cit. 
