612 DR R. K1DST0N AND PROF. W. H. LAND ON OLD RED SANDSTONE PLANTS 
Rhizome. (Plates IY-YI.) 
The rhizome of Hornea was of a different type from that of Rhynia, as will be 
evident from figs. 27 and 28 on PI. IY. It had no vascular strand of its own, but 
was a lobed parenchymatous body of considerable size, from which arose stems, each 
provided with a central stele. The stele of each stem ended separately and blindly 
below in the parenchymatous tissue of the rhizome (figs. 35 and 38). Numerous 
long rhizoids attached the rhizome to the peat. From its resemblance to the 
protocorm of the young plants of some species of Lycopodium , this type of rhizome 
may be distinguished as protocormous from the stem-like rhizome of Rhynia. The 
largest rhizome met with is represented at a low magnification ( x 7%) in fig. 31. It 
is branched, and at first sight appears of a different type, not being evidently lobed. 
It is, however, characteristic that no vascular system proper to the rhizome is seen. 
Comparison with the next section of the series showed that a number of stems arose 
from this rhizome, the plane of section in fig. 31 passing horizontally through the 
rhizome below the bases of the steles of these stems. 
The general structure of the rhizome is shown in the vertical section in fig. 29. 
The plane of section just misses the stem, and the rhizome appears as a massive, 
somewhat flattened body, about 8 mm. across by 2 mm. thick. It is composed of 
thin-walled parenchymatous tissue, between the cells of which are small intercellular 
spaces.* Towards the periphery the cells are somewhat smaller, and tend to be 
arranged in rows vertical to the surface, giving the appearance of an ill-defined 
outer cortex. The superficial layer constitutes a rather ill-defined epidermis, the 
small cells of which on the lower side of the rhizome bear the long rhizoids. 
The rhizoids, which are visible in a number of the illustrations (figs. 29, 30, and 38), 
are non-septate, and each is a protrusion of the middle portion of the outer wall of 
an epidermal . cell, from the cavity of which the rhizoid is not separated by a wall. 
Fig. 30 shows the rhizoid-bearing surface in vertical section, while in fig. 32 the 
surface is cut tangentially. Fig. 33 is a more general view of the latter section, 
and shows the long rhizoids extending from the small-celled epidermis. 
The structure of all the rhizomes shown on Pis. IV, Y, VI corresponds to that 
described above, some showing particular features more clearly. A number of them 
show the lobed form of the rhizome (figs. 27, 28, 35). In this connection the 
specimen in fig. 34 is of interest. A rhizome with a stem has apparently been cut 
obliquely, and two adventitious lateral growths had evidently developed from the 
superficial tissues as small protocormous rhizomes. The one shown in the figure 
bears rhizoids at rh. 
No vascular elements were present in the section of the rhizome in fig. 29, though 
some of the internal cells have peculiar brown walls, and in their neighbourhood the 
* The question whether the fungal hyplise which occur in the intercellular spaces of the rhizome are to be 
regarded as saprophytic or mycorhizic will be considered in a later paper when dealing with the fungi occurring in 
the Rhynie peat. Their frequent presence must, however, be mentioned here. 
