Weiss.- — A Mycorhiza from the Lower Coal-Measures. 259 
there is an indication of a phloem-sheath (fl.s.) or pericycle. The charac- 
teristics of these tissues are not well pronounced, and except for the 
xylem-groups the structure of the stele is somewhat unsatisfactory. 
The cortical tissues are well developed and consist of thin-walled cells. 
There is no such thickening of the walls as one frequently finds in the 
roots of Filicineae, nor any such specialized lacunar tissue as is typical 
of the stem and roots of most of the Lycopodiales, particularly of the 
Lepidodendraceae. 
It will be seen from Fig. 1 and Fig. 3 that some of the inner layers of 
the cortex are slightly more elongated in the radial direction, while the 
outer layers appear in the transverse section somewhat flattened owing to 
the tangential extension of the cells. It will be convenient, therefore, to use 
the terms exo- and medio-cortex for these two portions of the cortex 
in the same sense in which they have been used by Groom (’ 95 ) in his 
descriptions of the roots of monocotyledonous saprophytes where they 
show a similar differentiation. The difference between these two layers 
of the cortex can most readily be seen in the longitudinal section (Fig. 3) 
in which it will be further seen that the innermost row of cortical cells 
(endo-cortex, possibly endodermis) is drawn out longitudinally, while the 
tangentially and radially elongated cells of the exo- and medio-cortex are 
short, more particularly the latter. The radially elongated cells, as can be 
seen both in the transverse and in the longitudinal sections (Figs. 1 and 3), 
are also characterized by their very dark contents. These will be described 
in detail later on, but it may be mentioned at present that they show 
indications of fungal hyphae and closely resemble in their appearance and 
in their position in the cortex the curious contracted masses (clumps) 
described by various authors in the aerial roots of Orchids and in the 
absorptive organs (roots or rhizomes) of saprophytic Monocotyledons and 
of P silo turn. The exo-cortex, though also containing hyphae, possesses none 
of these ‘ clumps/ and consequently looks at first sight devoid of the Fungus. 
This specialization of the hyphae in two different regions of the cortex 
is a very common phenomenon in mycorhizae and is constantly met with 
in the plants mentioned above. Fungal hyphae are very rarely met with 
in the endo-cortex. Only in one transverse section were a few hyphae 
discovered in this layer. This, again, is in conformity with the behaviour 
of the fungal mycelium in the mycorhizae of living plants, and supports 
the conclusion I have arrived at, that the Fungus is not of a destructive 
nature ; or it would probably have penetrated into all the living tissues 
of the plant. 
The cells of the epidermis are smaller in size than the cortical cells 
as can be seen in Plate XVIII, Figs. 1 and 3, and are often drawn out into 
long absorptive hairs (Plate XIX, Fig. 2). This piliferous layer may 
possibly be regarded as evidence of the root-nature of the organ, but it 
