128 
H olden —Further Observations on the Wound 
(ii) The partial or complete degeneration, in the wound area, of the 
lignified elements constituting the sub-epidermal armour. 
(iii) A more or less pronounced thickening of the cell-walls, sometimes 
of a purely cellulose nature, but often accompanied by partial or complete 
lignification. 
Taking now the first of the two types of wound referred to above, it is 
found that the nature of the response is somewhat variable. Where the 
wound is extremely slight — that is to say, when the wound surface does not 
penetrate below the fourth or fifth layer of cells— there is very little obvious 
effect, except for the yellow discoloration alluded to. Microchemical tests 
demonstrate, however, that in the majority of cases the most superficial 
cells of the sclerenchyma have become delignified, and give the cellulose 
reaction with chlor-zinc-iodine. 1 If, on the other hand, the sclerised 
armour is almost penetrated, there is very generally a compensatory 
thickening of the cortical elements immediately below the wound surface, 
such thickening being normally of a cellulose or ligno-cellulose character. 
In about 20 per cent, of the cases examined, however, lignification appeared 
to be complete. These differences may of course be due to differences in 
the age of the wounds, but, judging from appearances, this is unlikely. 
The walls of the affected cells are abundantly pitted and do not appear 
in any way degenerate, except possibly for the yellow colour (cf. Fig. 1, v). 
The effect on the sclerised elements themselves, apart from delignification, 
is also of some interest, as in many cases a considerable increase in the 
thickness of the wall accompanies this process. This feature is well 
illustrated in Fig. 1, iii and iv, in which the walls of the sclerenchyma on 
the flanks of the wound show a marked increment which is entirely of 
a cellulose nature and is often obviously stratified. With regard to wounds 
of the second type, namely, those which penetrate the sub-epidermal 
sclerenchyma, the reaction is found to be extremely variable. In a large 
number of cases the plant exhibits merely a somewhat extensive local 
thickening of the cells in the affected area (Figs. 1, i, ii ; 2, i, &c.). The 
modified cells always extend more deeply into the tissues of the petiole in 
the neighbourhood of the vascular strands (Figs. 1, ii ; 2, ii), and in many 
cases the latter are wholly or partly flanked by patches of thickened 
tissue which are quite disconnected from the main mass (Figs. 2, iv ; 4, i). 
As in the less severe types of wound described above, the amount of 
lignification varies considerably, but the superficial uninjured cells practically 
always give a cellulose reaction, whilst those below stain pink or red with 
phloroglucin after acidification with HC 1 . The cause of the cellulose 
reaction of these more superficial cortical elements is something of a puzzle, 
but it may be that their nearness to the wound surface acts deleteriously 
upon them, and thus prevents their reacting as fully as those which are 
1 See Appendix. 
