314 Kisch . — The Physiological Anatomy of 
Lepidodendron selaginoides is particularly lacking in these tissues, but 
its periderm is far more conspicuously developed than in Lepidodendron 
Hickii or L . fuliginosum. It is conceivable that the large secondary cortex 
took the place of the defective storage tissue, and that this might account 
for its striking development in these plants. Such a function would also be 
consonant with the formation of the great quantity of thin-walled periderm 
found in the underground Stigmarian rhizomes, where, from their nature 
and position, the mechanical function must have been of secondary signifi- 
cance. It is also possible that the storage of food reserves was more 
specially the part of the strongly developed, regular, interior portion of the 
periderm of certain types, while the less crushable, outer, wide-celled layers 
had a more mechanical and protective part, and in this connexion were 
aided by the meristematic properties of the cells of the outer cortex, in the 
event of rubbing off at the surface, or other vicissitudes to which rhizomes 
in the soil may be subject. 
The External Manifestations of Periderm Development. 
(1) The Tissues outside the Periderm. 
As the periderm was not of the nature of cork, the tissues outside it do 
not dry up, but remain unchanged by its formation. This may be well seen 
by comparing a young Lepidodendroid stem without periderm with one in 
which it has attained considerable development. The cells of the leaf-bases 
and outermost primary cortex present the same appearance in both cases, 
and occasional divisions continue to take place. In some Stigmariae it has 
been seen (p. 294 ) that such divisions are very frequent. 
The tissues outside the periderm do not show much sign of tangential 
stretching, except sometimes in the angles between adjacent leaf-bases, and 
must be able to keep pace with the growth of the circumference. Among 
the intact specimens examined, the leaf-bases are still persistent with the 
following developments of periderm : 
Lepidodendron selagmoides about 200 rows of periderm cells. 
„ Harcourtii 
33 
120 
33 
33 
„ Hickii 
33 
20 
33 
33 
„ Wunschianum 
5 3 
20 
33 
33 
„ brevifolium 
)} 
30 
33 
33 
„ obovatum 
5 ? 
50 
33 
33 
„ fuliginosum 
>5 
35 
33 
33 
„ Scottii 
3) 
60 
33 
33 
„ sp. ( Lepidophloios ) 
33 
5o 
33 
33 
Sigillaria scutellata 
33 
120 
33 
33 
„ elegans 
33 
80 
33 
33 
„ sp. 
33 
50 
33 
33 
