Reactions of the Petioles of P ter is ctquilina . 133 
was left, and this had thickened considerably (Fig. 1, vi), whilst of the 
strand C about half remained. In this the starch sheath had also thickened, 
and in addition elongation of the cells had occurred on the side remote from 
the wound surface (Fig. 1, vii). The remaining xylem and sieve-tubes 
showed a bright yellow coloration, and there were some indications of 
elongation in the case of the conjunctive parenchyma. A further illustra- 
tion is afforded by the vascular bundles shown in Fig. 4, i, ii, and iv. The 
reaction only affected one end in each of the two bundles and, as in the 
previous instance, the elements composing the starch sheath had elongated 
and thickened, but in addition many of the cells had divided by a transverse 
wall. The conjunctive parenchyma was much more obviously active in the 
smaller and more superficial strand than in any other instance noted. 
Many of the cells were thickened and displaced, and in one small portion, in 
which the cells had remained thin-walled, a small cambiform patch was 
developed. All the thickened cells were bright yellow with tannin, and 
gave a cellulose reaction. 
One other point remains to be mentioned, namely, the absence of the 
gum deposit which was so constant a result of the traumatic stimulus in 
artificially wounded forms. 1 In the present series, gum deposits only 
occurred in the cavit}^ parenchyma of affected bundles and in occasional 
tracheides. Apart from this one feature, the examination of the petioles 
confirms the results arrived at experimentally in the earlier paper with 
regard to ferns of the type of Pteris aquilina . 
Summary. 
1. Petioles of wild Pteris aquilina often show wound-scars. The majo- 
rity of the wounds are very superficial, not penetrating the sub-epidermal 
sclerenchyma ; others are deeper seated. 
2 . The wound reactions are somewhat variable, but are characterized 
by (i) a compensatory local thickening, and partial or complete lignification 
of the cortical parenchyma, which may or may not be accompanied Ty 
elongation, (ii) the local delignification of the sub-epidermal sclerenchyma, 
(iii) a deposit of tannin in the cell-walls in the affected area. 
3 . Wound reactions in the tissues composing the vascular strands are 
rare, and where they do occur are confined to the starch sheath and con- 
junctive parenchyma, which thicken and may elongate and divide. 
4. The results obtained are confirmatory of those produced experi- 
mentally. 
1 Holden, loc. cit. 
