A Wounded Myeloxylon, 
256 
very similar in appearance to a true periderm such as is found in 
the early stages of cork formation in woody dicotyledons or perhaps 
even more closely resembling the tissue situated immediately below a 
lenticel. This appearance suggested the possibility of the structure 
actually representing a lenticel, but the fact of its being the only 
case recorded of cambial tissues in a Medullosan petiole is all 
against this view, and a comparison with the lenticels found in the 
Marattiaceac and Cyathacese again shows very little similarity. It 
will thus be seen that this view is untenable and that the only one 
in accordance with the facts is that it represents a true periderm. 
It would thus appear that these series of cells, which become 
successively less compressed as they get more distant from the 
periphery, are the result of the continued division of the cortical 
cells immediately below the seat of the injury, a feature which one 
might expect since the plant, to avoid excessive loss of water would 
naturally produce a layer of protective tissue in that region, as 
rapidly as its abilities permitted it to do so. Below this layer the 
original cortical cells are still, in places, distinguishable, but are 
subdivided into groups of from three to five cambiform cells still 
forming an almost continuous band of meristematic tissue 
(Figs. 18 a and 18 b). 
Proceeding ftom the seat of injury towards the centre of the 
petiole it is seen that the continuity of this zone becomes more and 
more interrupted until it is represented by an isolated cortical cell 
here and there showing subdivision into two parts only, and about 
the region of the first bundle-ring all evidences of abnormality 
disappear. 
Cases of periderm formation among the Ferns are apparently 
somewhat rare, but they are referred to by Brebner who records 
them for the Marattiacese and also in a later paper by Chandler, 
the latter of whom gives a figure. A comparison of this with the one 
forming the subject of the present note reveals a striking similarity, 
though the cases are not absolutely parallel, since the former 
(Ann. Bot., XIX., PI. XX., Fig. 208) represents a typical case of 
periderm formation in a rhizome, not a petiole. Periderm is also 
mentioned as occurring in the case of wounds in the rhizomes of 
the Ophioglossaceae by De Bary in his opening paragraph on 
“Cork-formation,” and also by Holle. 
In conclusion the writer’s acknowledgements are due to 
Professor F. E. Weiss, for much kindly help, to the Museum 
authorities for permission to describe the slide, and to Mr. Alex. 
