312 
Kisch.— The Physiological Anatomy of 
{ JA 'MV/- NJ 
lx n' ) 1 
zones may also be traced in vertical sections (Text-fig. 24, b) ; they have 
been described and figured by Seward and Hill. 1 
In Stigmariae the periderm is sometimes zoned by layers of very much 
crushed or broken-down cells (Text-fig. 25), and between these zones there 
are, in a few specimens, darker-coloured groups arranged more or less in rows. 
As to the nature of all these zones, Hovelacque regarded them in 
Lepidodendron selaginoides as less resistant layers formed at periods of 
sluggish growth, 2 but more recently much stress has been laid upon their 
interpretation as secretory strands. This function was first ascribed to the 
concentric bands of cells in the periderm of 
Lepidodendron Wunschianum , 3 and was then 
extended to the zones of Lepidodendron selagi- 
noides l while it has been suggested that possibly 
the zones in Stigmaria 5 and Syringodendron 
esnostense 6 should be included in the same 
category. In Lepidodendron Wunschianum it 
is stated that ‘ at fairly regular intervals groups 
of the phelloderm cells underwent further 
division, and constituted definite strands of 
secretory cells ’, which, when disorganization 
is more advanced, consist mainly of 4 oval and 
circular areas, which may be either empty or 
occupied by portions of thin-walled cells and 
products of secretion ’. They are said to be 
probably lysigenous in development, and their 
appearance is compared with that of the resin- 
canals in the wood of Conifers and in Copaifera 
Langsdorffti? 
It should be noted that in the outer 
primary cortex of several species, including 
Lepidodendron Wunschianum , Harcourtii , fuliginosum , Bothrodendron , and 
Xenophyton , there are groups of cells which have been very generally 
interpreted as internal glands. It cannot be said, however, that the 
zones in the periderm show the distinctive character of secretory tissue. 
Although lysigenous glands in recent plants are surrounded by the remains 
of dissolved or obliterated cells, and not by an epithelium, yet their distin- 
guishing feature is the formation of a passage, which starts in a single cell 
and proceeds in the centrifugal direction. 8 But in the zones of these peri- 
derms cavities are by no means general, even in the old specimens which 
1 Seward and Hill (29), p. 916, Figs. 2, 3, 12, 18, and 31. 
2 Hovelacque (15), p. 58. 3 Seward and Hill (29). 
4 Seward (28), pp. 118, 121. 6 Seward (28), p. 244. 
6 Seward and Hill (29), p. 925. 7 Seward and Hill (29), p. 916. 
8 Tschirch (31), p. 508. 
Text-fig. 25. Stigmaria sp. 
Zones in the periderm. Will. 
Coll., 766. x 55. 
