4 MR. 8. G. SHATTOCK ON THE REPARATIVE 
living parts, subjected to ordinary expo- 
sure, come to be nevertheless protected. 
I have noticed that in the earlier stages 
(such as may be seen fourteen days after 
the injury) the only change shown by the 
microscope will be that several tiers of the 
original elongated cells beneath the divided 
surface appear sharper in outline than 
those of the general substance, the altered 
layer being of uniform thickness and well 
defined from the rest of the parenchyma 
beneath, in whieh there may be in spots 
evidences of transverse partitioning. That 
the layer of altered cells has acquired new 
characters is shown by treating the section 
with iodine and sulphurie acid: whilst 
the general parenchyma is stained deep 
Fig. 1. 
blue, these layers of surface-cells remain Section of Echalium agreste. 
uncoloured, their walls having undergone a 
protective suberous change, though their 
elongated form shows these cells to be 
original elements of the petiole. This 
chemical change in the outer com- 
ponents of what is in its origin a 
single structure, may be compared 
in animal textures with the change 
in the outer cells of the cuticle, 
which are horny and not colourable 
with logwood, whilst those more 
deeply seated are wholly, or in part, 
of different composition and readily EE 
stained. 
the surfaces made by removing the 
Amputation through base 
of young petiole, repair 
after fourteen days, show- 
ing partitioning of the 
cells a short way beneath 
the surface. 
S< 
Similar changes are observable in m d e > 
the stems of Datisca cannabina, in 4 
portions which support the growing = C QUE C 
leaves. A thick layer of cork is 
formed of the original cells, most of Section of Datisca cannabina. 
which undergo subdivision to the 
second or third degree, forming 
short tiers of cells irregularly packed 
Amputation through base of 
young petiole, 
six weeks. 
line the tissue is suberous, the 
more superficial cells being un- 
repair after 
Above the dotted 
changed in form, the deeper 
subdivided. : 
