OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 
1G3 
I have several transverse sections of this root in my cabinet, one of wliicli is 
represented in fig. 17 (Plate 4). In its centre is a vascular bundle, a, having a 
somewhat irregular triangular section. This is invested by a zone of delicate 
parenchyma, h. An enlarged representation of the transverse section of this bundle 
is given in fig. 18 (Plate 3). On the upper side of fig. 17 are long sections of five, 
c, c, c, c, c, of the radiating secondary rootlets of the vertical axis from the cortical 
layer h', of which they are extensions. Two similar specimens indicate that there 
were from ten to eleven rootlets in each such verticil. As the cells of the cortex h 
are prolonged into each rootlet they become elongated radially. Fig. 18 indicates that 
the central bundle of fig. 17, here further enlarged, is a triangular one. Fig. 19 
represents a similar bundle of another transverse section like fig. 1 7, and enlarged 
equally to fig. 18. It exhibits in a similar way the bundle a, surrounded by its 
investment of either procambium or phloem. It is obvious, therefore, that the trans¬ 
verse section of the primary bundle of this root was triangular, presenting at least 
all the essential characteristics of a triarch root. I would distinguish this plant, 
which, like that last described, is also fi’om Halifax, by the provisional name of 
Rhizonium verticillatum .^ 
Whatever may be the case with figs. 17 and 18, I think there can be no doubt 
that fig, 20 is a transverse section of a true triarch root, enlarged 42 diameters. 
Fig. 21 represents the centre of the same section still further enlarged ; a is a 
triarch vascular bundle ; h, a concentric phloem; d, cycloidally arranged cells of 
the cortex. 
Fig. 22 (Plate 3) is an obliqpe transverse section of a cylindric rootlet of another 
description ; at a a few vessels or tracheids occupy the centre of a mass of delicate 
elongated cells, either representing phloem or procambium. The middle cortex, h, 
consists of a loose form of parenchyma, enclosing numerous irregular large lacunse of 
the type so common in the roots of the Nymphese. Of course, this indicates no 
systematic relation with the latter plants, beyond the fact that our fossil root most 
probably belonged to some aquatic or semi-aquatic type. At c is a compact quasi- 
epidermal investing layer of cells. The specimen, which is from one of the Oldham 
nodules, may be designated Rhizonium reticulatum. 
Fig. 23 (Plate' 3) is a somewhat larger rootlet, also with a lacunar cortex. A 
strongly defined vascular cylinder, b, encloses a delicate medullary parenchyma a, 
and is invested by a compact zone consisting of several cycloidally arranged rows of 
* I was at first inclined to include these root-like objects in my provisional group of Rachiopteris; 
but, since they present few or no indications of being either rhizomes or petioles, I have determined to 
utilise Corda’s term Bhizonium for them. Corda’s objects, to which he gave this generic name, he 
appears to have regarded as being probably the roots of Orchidaceous plants ; but they are really irndis- 
tinguishable from the rootlets of Stigmaria ficoides. Corda’s definition of his genus, “ Radiculse para- 
siticse, intertext®, cortice parenchymatosa ; fascicule vasorum solitaris central! vagina propria inclnso ” 
(•Flora der Vorwelt,’ p. 46), is, with the exception of the two first adjectives, fully applicable to my 
plants.—February 12th, 1889. 
