296 Kisch. — The Physiological Anatomy of 
may be seen rather delicate-looking cells and traces of broken cell- 
walls. 
Lepidodendron Wunschianum. Seward and Hill assumed that the 
secondary cortical tissue was all phelloderm, 1 but the outer margin is 
not preserved. The inner margin certainly shows no sign of the presence 
of meristem. 
Lepidodendron fuliginosum . Weiss assumed that the secondary cor- 
tical tissue was all phelloderm. 2 Seward states that it is chiefly so. 3 
Lepidodendron Scottii. 
Bothrodendron mundum. 
Sigillaria tesselata. 
Sigillaria spinulosa. In an allied species Renault and Roche speak 
of the internal renewal of the periderm layer. 4 The material available for 
the present paper did not show either margin of .the secondary cortical 
tissue, but it will be shown later (p. 307) that it is more probable that the 
phellogen was on the outer side. 
In an examination into the physiological anatomy of the periderm, this 
question as to the position of the phellogen in the tissue would seem to 
be of the greatest importance. It may therefore be stated at once that, 
whatever the morphological nature of the secondary tissue, there is no 
evidence to show that any of it was other than secondary cortex, even when 
some portion is formed on the outer side of the phellogen. It is probable 
from the whole nature of the periderm and its formation that in the fossil 
Lycopodiales there was not that strict division of labour which so sharply 
differentiates the cork from the phelloderm in the periderm of gymno- 
spermous and dicotyledonous plants. If this is so the direction of the 
divisions (i. e. centripetal or centrifugal) is no longer connected with difference 
in function, and becomes a matter of minor significance. 
(5) Persistence. 
In the species examined the original phellogen was persistent, at least 
up to the time of preservation, and was not, as in so many recent plants, 
replaced at intervals by the development of a more internal phellogen. 5 
Arber and Thomas have suggested that it was of a periodic nature, at any 
rate in Sigillaria scutellata , on account of the difficulty in distinguishing 
a definite cambial layer, and of the presence of concentric zones in the peri- 
derm, which they interpreted as rings of growth. 6 When it is remem- 
bered, however, what a very large number of specimens show no definite 
phellogen, and that only a few of these are at all regularly zoned, it 
1 Seward and Hill (29), p. 917. 
3 Seward ( 28 ), p. 153. 
5 With one possible exception (see p. 317). 
2 Weiss ( 33 ), p. 229. 
4 Renault and Roche ( 23 ), p. 17. 
6 Arber and Thomas ( 1 ), p. 141. 
