301 
the Periderm of Fossil Lycopodia les. 
tracheides , 1 while in a recent paper Zalessky speaks of the 4 stries spiraUes ’ 
seen in vertical sections of the periderm of his Lepidodendron obovatum? 
As regards the thickening substance, one can say with certainty that 
it was not suberin. The walls of the secondary cortex must have been 
permeable to water, for, whenever the tissues outside are preserved, they 
show none of the characteristic signs of arrested activity and collapse pro- 
duced in cells isolated by a zone of cork. The impossibility of the periderm 
being of the nature of true cork has been pointed out several times, chiefly 
in regard to Stigmarial though other writers who have recognized it as 
phelloderm have spoken of it as being cork-like in function , 4 or as having 
Text-fig. 13. Transverse sections of certain periderm cells showing local swelling of the walls. 
A, Lepidophloios sp. U. C. L. Coll., A 32. B, Lepidodendron selaginoides . U. C.L. Coll., A 0121. 
x 265. 
some suberized layers . 5 It should perhaps be mentioned that the cork 
crusts of some recent plants do not always have suberized walls, e.g. Ulmus 
suberosa , but the quantity produced makes up for defects in quality, and 
many of the cells are true cork . 6 In the plants under consideration the 
cortex nature of the periderm is confirmed by other qualities, and, though 
it may have contributed to the protection of the interior tissues, this was 
probably quite a secondary function . 7 
(5) Cell Contents. 
The cells of the periderm of nearly all the species show as much sign 
of contents as the adjacent cortex, and there are therefore no indications 
1 Weiss (36), p. 223; Seward (28), p. 242. 2 Zalessky (47), p. 5. 
3 By Williamson and Solms, and later by Scott and Seward. 
4 Weiss (33), p. 229. 5 Arber and Thomas (2), p. 514. 
6 See Haberlandt (13), p. 125, 4th ed. 
7 Two cases of wound periderm in the fossil Lycopodiales have been mentioned, by Seward (27) 
and Weiss (34), but none has been examined in the present investigation. 
Y 
