6 MR. S. G, SHATTOCK ON THE REPARATIVE 
so as finally to be completely separated, The surface will then 
appear silver-grey, dry, shining, and membranous ; and contrasting 
with the earlier stages, both the ground-substance of the cortex 
and the pith are slightly convex, the zone of dead wood and 
bast being hidden in the furrow between. The new surface re- 
sembles in all its characters the general surface of the stem; and 
a microscopic section shows the central and peripheral paren- 
chyma to be invested with a uniform layer of flattened suberous 
cells, closely arranged in tiers and set in rows on the subjacent 
surface. The new layer is continuous at the margin with the 
deeper part of the periderm. 
The same steps of cork-formation may be here observed as were 
before noticed. A section treated with iodine and sulphuric acid 
will show, forming the actual surface, a crust of the original 
unaltered cells, dead, stained blue (as dead cellulose is), and still 
erammed with starch; beneath this the elements cease to give 
the cellulose reaction; and the cells are traceable in various 
phases of cross-multiplieation, from the simplest most outwardly, 
with increasing degree and regularity, till the dividing paren- 
ehyma has produced a considerable thickness of tabular corky 
cells resting on an ordinary phellogen, the cells of which pass by 
gradations into the general parenchyma. 
This is the ordinary mode of repair. But there may be added 
a formation of sclerenchymatous tissue in the pith a short dis- 
tance beneath the flattened growth of cork described, the ground- 
tissue of the pith producing secondary meristem of elongated cells 
set across the axis of the amputated branch, the deeper of which 
cells undergo thickening and conversion into woody parerchyma. 
The medulla in such a case is closed by a dome of hardened tissue 
continued into the wood at its margin. The process recalls the 
closing of the medullary canal ofthe bone in an amputation-stump 
by new osseous tissue. The cap of new bone in such circum- 
stances may be formed in the substance of the granulations which 
grow from the exposed medulla, though at other times it is pro- 
duced in an intermediate fibrous membrane; and in the case 
which I have described the sclerosed tissue is formed of the in- 
different cells of the pith and those to which these cells give 
rise. 
Somewhat similar results are observable after the removal of 
branches in Aucuba japonica and the fleshy stems of Cactace&. 
In Cereus the surface of an amputation is repaired as follows :— 
