299 
the Periderm of Fossil Lycopodiales. 
(see Text-figs, io and n, a ; PI. XXIV, Figs, i and 2, &c.). Often there are 
files which do not quite reach to the outer border of the secondary tissue ; 
then there are some files which taper away before reaching the inner 
margin, and, in a few species, also some which at neither extremity reach 
the border of the periderm. 1 In Stigmariae the arrangement is specially 
irregular. The appearances produced are probably due to various causes. 
The files may not all run continuously in the same horizontal plane ; or if 
the sections are not quite transverse, new files get cut across at intervals, 
first at the narrow ends of the cells, and then in the wider parts, while 
correspondingly other files gradually pass out of the section (Text- 
fig. 10, b). Then again the periderm may not have originated in 
a single layer of cells at the same level (Text-fig. 10, A, and Text- 
Text-fig. ii. Transverse sections from the outer part of the periderm of Stigmaria (type 2% 
A, irregular tangential divisions at a. B, recently formed radial septa forming a new short fde, r. 
U. C. L. Coll., CC 7 h. x 90. 
fig. 4) ; and further irregularity is caused by radial divisions in the phellogen 
to keep pace with growth (see Text-fig. 5), and possibly also by displace- 
ment. 
It appears probable that in some cases short files may be produced by 
subsequent division of the cells of the periderm (Text-fig. 10, c). This 
would help to account for the very irregular arrangement in Stigmariae 
(PI. XXIV, Figs. 1 and 2), and recently formed radial septa may be traced in 
places (Text-fig. 11, B). In the wide-celled type of Stigmarian periderm 
further tangential divisions may also take place (Text-fig. 11, a), as was men- 
tioned on p. 294, and many of the cells of the cortex outside the periderm 
may start to divide (PI. XXIV, Fig. 2, e), producing additional files, and 
1 Similar short files may be found in transverse sections of the secondary wood of these plants. 
