CouTANT: Woop PERIDERM IN CERTAIN CACTI 363 
DIsCUSSION AND CONCLUSIONS 
The series of changes which take place after injury, as described 
in the different ages of the wounds, really gives in itself a summary 
of what reactions took place. 
The disappearance of starch in certain cells of the cacti prior 
to normal cork formation, is noted by Soraurer (5, p. 428), so it 
is not surprising to find it here, prior to the development of wound 
periderm, which, as can be seen, greatly resembles that produced 
normally. 
This latter fact was noted by Schleiden (3, p. 353) who states 
that the best analogy to the natural cork building process is seen 
in the effect of wounding, and that this can be observed nowhere 
so easily as among the cacti. He does not, however, go greatly 
into detail, but describes the “drying up” of the cells on the 
surface of the wound, due to the ‘‘evaporation of their liquid 
contents” and says that this layer of ‘“‘dried out”’ cells forms a 
protection to the cells underneath, out of which is formed the cork. 
He also states that the wound formation does not take place 
exclusively in cells exposed to air, but in behalf of this, gives no 
convincing proof. 
Kiister (1, p. 186) in his work on the histology of wound-cork, 
says that the walls are always thin, and often folded, and that 
differentiation of any kind whatsoever is entirely absent. This, 
of course, is not the case in these cacti. The formation of the 
thick-walled lignin cells is in itself enough to disprove the fact. 
The essential new facts brought out by this paper are (1) the 
lignification of the old outer cortical cells, (2) the production of 
both thin- and thick-walled cells by the activity of the wound 
phellogen, and (3) the formation of the second interior meriste- 
matic layer, forming the new vascular bundles, parallel to the 
wound surface. 
I wish to thank both Dr. D. T. MacDougal, of the Carnegie 
Desert Laboratory at Tucson, and Dr. H. M. Richards, of Barnard 
College, for their kindness in providing me with material, and to 
express my sincerest appreciation to Dr. Richards for the aid 
he has given me in my work. 
BARNARD COLLEGE BOTANICAL LABORATORY, 
CotumsBiA UNIVERSITY 
