780 Holden. — Some Wound Reactions in Filicincan Petioles. 
It is a well-known fact that the tissues of many fern petioles are, even 
at maturity, of a comparatively delicate and parenchymatous character, 
a feature which is shared by all forms in their extreme apical portions, 
whilst others, such as Osmunda regalis and Davallia polyantha , are charac- 
terized, when mature, by an extremely tough, almost horny exterior, 
together with a highly developed sub-epidermal band of sclerized tissue, 
this rendering them very resistant. This tough character is doubtless 
a necessity in the large, upstanding forms, but is by no means confined to 
these, several of the small forms (e. g. Adiantum spp.) showing similar 
characters. 
It appeared to the writer that, in this difference in the character of 
the more mature parts of the petiole, there occurred one of the features 
which lent itself to the grouping of the forms worked upon, and this proved 
to be the case, for it was only in what might be termed the softer bodied 
forms that any appreciable cell-growth, in response to injury of the maturer 
parts, occurred. 
(i) Taking first the curled, apical region, it was found that practically 
the whole of the forms experimented upon showed attempts at cambium 
formation. This, in the most successful cases, resulted in the production of 
a complete wall of meristem in the injured area, and was found to occur in 
only a small number of the species examined, namely, Asplenium Belangeri , 
A. bulbiferutn, A. viviparu rn , P olystichum prolifer u in, Woodwardia orientalis, 
and IV. radicans. A reference to the figure (PL LXXIII, Fig. 1) illus- 
trating the wound meristem produced in the case of P olystichum prolifer um 
will serve to demonstrate the complete nature of the healing. Here the 
wounded area has been completely traversed by an entirely new growth, 
several cells in depth, of typically cambiform cells with delicately granular 
contents. This growth is due to the elongation and division of the layers 
of cortical parenchyma abutting upon the wound, and has, in a few cases, 
rendered the identification of these primary units difficult, though in most 
parts the outlines of the original parent cells can still be determined. 
The result of this continued elongation and division has been, in 
favourable cases, to produce at the originally flat, or slightly concave wound 
surface, a distinct convexity or intumescence (PI. LXXIV, Fig. 20). The 
mode of growth of the affected cortical cells is well shown in specimens which 
have been allowed to grow for some time (nine or ten weeks). In these it 
is clear that the elongation is accomplished by a process of sliding growth 
somewhat analogous to that obtaining in the development of prosenchyma- 
tous elements, and often results in the production of a row of cambiform 
cells, of which the terminal members are somewhat longer than their fellows, 
and are bluntly conical in shape, thus enabling them to dovetail into the 
spaces between the divergent ends of their neighbours (PI. LXXIV, Fig. 19). 
A peculiar feature with regard to the cambial cells which lie at the 
