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the Periderm of Fossil Lycopodiales. 
L epidodendron selaginoides, where apparently a single layer of cells starts to 
divide (Text-fig. 4), but even here it seems probable that some of the 
secondary elements formed sometimes divide again. Text-fig. 4 shows the 
typical appearance of the flattened, thin-walled cells of the phellogen. 
In other cases, as in Lepidodendron Hickii , Bothrodendron , and some 
young Lepidodendron species, the phellogenetic divisions may clearly be 
Text-fig. 5. Transverse sections showing phellogenetic divisions starting in several layers of 
cells. A, Lepidodendron sp. Will. Coll., 1922 E. B, Lepidodendron Ilickii. Will. Coll., 380b. 
C, another Lepidodendron sp. U. C.L. Coll., A 49. D, Bothrodendron mundum. U. C. L. 
Coll., A 014. Slightly diagrammatic. X 265. 
seen starting in several layers of cells (Text-fig. 5), sometimes in two cells 
on the same radius. 1 The periderm of other species, of which there are no 
young examples, appears to have been similarly derived from this type 
of phellogen. 
1 Watson (loc. cit.) noted this in L. Hickii , and thought it might mark the beginning of a 
secretory passage, but there seems no reason to suppose this, especially as no such passages have 
been found in this species. 
