ORGANIZATION OF THE FOSSIL PLANTS OF THE COAL-MEASUBES, 719 
bands of sclerenchyma and parenchyma, constituting the characteristic Ductyoxylon 
cortex, as it is called by Count Sozms-Laupacu. The cortex may be passed over 
in few words, as its structure has been sufficiently described in former memoirs. 
It must, however, be pointed out that ‘‘the inner parenchyma of the bark,” described 
in Memoir IV., p. 382, includes both phloém and pericycle, in addition to the inner 
cortex of our present description. The specimens discovered up to 1872 were not 
sufficiently well preserved for all the zones to be distinguished. 
The inner cortex presents little of interest ; it is generally the worst preserved part 
of the stem, although its cells had somewhat thicker walls than those of the peri- 
cycle. Its frequent disorganization in specimens otherwise perfectly preserved (see 
Plate 18, photograph 1) may be an indication that it had begun to die off in consequence 
of the formation of internal periderm while the plant was still living. For the 
structure of this layer, see Plate 21, fig. 1, and Plate 18, photograph 4. In some of the 
specimens many of the cells seem to have collapsed, giving the appearance of a tissue 
with larger elements than actually existed.* 
The secretory sacs are specially abundant in the inner cortex. We rarely find 
sclerotic nests in this region except at the bases of leaves, where they are very 
numerous (see Plate 18, photographs 3 and 4, and Plate 23, fig. 10), and whence they 
extend into the cortical tissue of the petiole. As regards the outer cortex the only 
point which need be mentioned is the great tangential dilatation of the parenchy- 
matous bands, owing to the secondary growth in the interior of the stem (see 
photograph 1 and fig. 1). This dilatation, which reaches its maximum in the outer 
cortex, applies to all regions external to the cambium. In some cases it is very 
conspicuous in the pericycle, where it sometimes leads to a wide separation between 
the two bundles of a leaf-trace. Secretory sacs occur in the parenchymatous portions 
of the outer cortex. As already mentioned, a few layers of tissue are sometimes 
preserved to the exterior of the “ Dictyoxylon” zone. The remarkable outgrowths 
or emergences which arise on the outer surface of the cortex have been fully described 
and figured in Part XVII., Plate 12, figs. Land 6. They each consist of a sclerotic 
envelope enclosing a parenchymatous core, these two tissues being continuous with 
the corresponding parts of the external cortex. ‘The apex of the outgrowth is blunt. 
The emergences (for they are certainly too deep-seated to be called hairs) are by no 
means equally frequent in all the specimens; in many cases they probably became 
detached, together with the superficial cortical layers. Very similar appendages are 
found on some recent tree-ferns, as Alsophila armata, and more especially Alsophila 
australis, in which the blunt spines are much like those of Lygunodendron. In these 
ferns the spines are surmounted by pales, which soon become detached, but whether 
this was the case in Lyginodendron also cannot be determined. 
The emergences have played an important part in the scientific history of the plant, 
* See Wittamson, “Organization,” Part XVII. Plate 13, fig. 3. 
