294 Kisch . — The Physiological Anatomy of 
periderm, that the section had split off along the phellogen, so that the 
secondary cortical tissue preserved was formed on its outer side . 1 
(b) Stigmariae. The periderm of the Stigmariae presents at least two 
distinct types. 
Type i. The periderm is fairly regular in appearance (PL XXIV, Fig. i), 
and seems to have been developed on the outer side of the phellogen. 
Only part of the periderm is generally preserved, and there are cambial- 
looking cells along its inner margin (see Text-fig. 9, A. ph). When, in rare 
cases, the whole of the periderm is present, the inner layers are seen 
to consist of very delicate and thin-walled cells which pass imperceptibly 
Text-fig. 8. Sections showing indications of the position of the phellogen near the outer 
margin of the periderm. A, transverse section of Lepidophloios sp. Will. Coll., 1955. B, radial 
section of Lepidodendron fuliginosum. U. C.L. Coll., A 33. C, transverse section of Sigillaria 
elegans. ph , phellogen ; c, cortex outside periderm. U. C. L. Coll., E 5 a. a and c x 265, B x 90. 
into the primary cortex. This is shown in PL XXIV, Fig. 1. At x a cell 
may be seen which has just divided. 
Type 2. The periderm consists of a very irregular, wide-celled outer 
portion (PL XXIV, Fig. 2, a), of which many of the cells retain the power 
of division and which may receive additions from the division of cells 
of the outer cortex, and a more regular and smaller-celled internal portion 
(PL XXIV, Fig. 2, b). This latter, which may greatly exceed the outer 
portion in thickness, is usually broken off abruptly on the inner side. In this 
type, though a disorganized band of cells is all that can generally be distin- 
guished, the phellogen is probably at the junction of the two different kinds 
of tissue (PL XXIV, Fig. 2 ,/A), and forms the wide cells to the exterior and 
the narrower files on its inner surface by means of further radial divisions. 
Occasionally these divisions may lapse, and a wide-celled file extend some 
1 Seward (28), p. 109. 
