OF THE FOSSIL PLANTS OF THE COAL-MEASUKES.

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of long, narrow, square-ended cells of variable length and about '0005 in diameter; butinterspersed amongst them are many scattered cells of larger dimensions, as shown in fig. IB.

Cortex. —External to the vascular bundle-sheath we have a thick mass of ordinaryparenchyma, figs. 4, e, 14, e, & 20, e, the cells of which are remarkably uniform, both intexture and size, their diameters chiefly ranging between '005 and •003. This paren-chyma is invested by a thin outer layer about ’04 in thickness (figs. 4, /, & 2 ,f), com-posed of denser and darker-coloured cells.

Secondary bundle. —I have already remarked that, besides the large central vascularcylinder, each transverse section of the stem reveals two or more secondary bundles.Of these the largest and most conspicuous is the usually solitary one of this type repre-sented in fig. 4, c ; and in the subsequent figures the same bundle is indicated by thesame italic letter. An enlarged representation of this bundle, as it appears in thesection, fig. 4, is seen in fig. 17. Its outline is reniform. The greater part of thevessels, g, of which it is composed are nearly as large as those of the central cylinder ; butthose seen clustered together at each extremity of the transverse section, g 1 , are very muchsmaller than the others. This vascular bundle is surrounded by a sheath of narrowelongated cells (fig. 4, g"), identical with that investing the axial cylinder, and this, inturn, is enclosed within the ordinary parenchyma of the inner cortex (fig. 4, c).

The origin and destination of this bundle would be alike obscure were our study of itlimited to a single section; but by following the ascending series of sections included in thefigures 2-12 we obtain information on both these points. In the sections from figs. 2-8, c,we see but little change in the position and surroundings of the bundle; but in fig. 9we find that the outermost cortical layer of the stem (fig. 9, f) is obviously bendinginwards at two points tending towards the enclosure and detachment of the bundle

from the main stem. In fig. 10 this enclosure is complete. The bundle c is now thecentre of what has every appearance of being the base of a leaf-petiole. In fig. 11, c,the bundle has been accidentally broken away in the preparation of the section; but atf' we find the petiole freeing itself from the central stem, whilst in fig, 12 the part ofthe stem, f', from which the orientation took place is now encircled by the normalinvestment of outer cortex. In its original state the outer surface of the specimenexhibited several rounded areas not marked by defined cicatrices, but irregularlyfractured, from which points similar petiolar extensions seem to have been broken off.Fig. 18 represents a section of one of these detached petioles enlarged 7ij diameters.I am indebted for this section to Mr. Butterwortii, by whom it was prepared. Itscentral vascular bundle ( c ) is virtually identical in size and contour with that of fig. 17,whilst the inner (e) and outer (f ) cortical layers are, in like manner, identical with thoseof the parent stem. The large rounded lacunae in the inner bark are merely accidentalresults, probably of partial desiccation before the specimen was imbedded in its matrix.

Origin of the primary bundles. —On returning to the series of sections, we observethat at the point V of fig. 6 the central vascular cylinder is undergoing a change. Thearrangement of the tissues at this point is seen in fig. 19, which is an enlarged repre-

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