260 Weiss.— A Mycorhiza from the Lower Coal-Measures. 
must be remembered the rhizome of Psilotum and Tmesipteris , as well 
as some of the modified absorbing rhizomes of saprophytes, bear such hairs. 
It is indeed difficult, as Groom (’ 95 , II) has shown, to distinguish between 
roots and rhizomes in these plants, as they may be very considerably 
altered both externally and internally. Not only may the leaves be 
considerably atrophied but, as Groom points out, c the structure of the stele 
in absorbing rhizome-axes of hemi- and holo-saprophytes is frequently 
remarkably like that of a root (Corysanthes, Burmannia , Corallorhiza :), so 
the root-like structure of the stele of the absorbing organ is no proof of its 
root-nature/ It would seem, therefore, best to suspend our judgement with 
regard to the nature of the organ in question, and similarly we shall have 
to remain in doubt as to the systematic position of the plant until other 
portions of it have been discovered. 
The Fungus. 
The general distribution of the mycelial threads within the host-plant 
has been mentioned above as well as the different appearance of the 
Fungus in the exo-cortex and medio-cortex respectively. In the epidermis 
too hyphae may be noticed, but their occurrence in a cell does not 
necessarily mean that this has been a centre of infection. Sometimes, 
as in the cell bearing a root-hair in Plate XIX, Fig. 2, hyphae may be 
running longitudinally through the cell. Sometimes, however, numerous 
hyphae are seen running radially across the epidermal cells ( h in Fig. 2) ; 
but in no case have I been able to trace them beyond the outer wall. 
Even in such cases, however, we have no proof that it was through these 
cells that the Fungus had gained admission, as it is known that hyphae 
may grow out from the mycorhiza into the surrounding medium. Thus 
Groom (’ 95 , II), in his description of Thismia , mentions (p. 354) that it is 
possible to observe ‘ that frequently free hyphae are deserting, not entering, 
the host-plant.’ Whether the particular hyphae shown in Fig. 2 are 
entering or leaving the tissues must of course remain an open question 
in the case of a fossil plant. 
In the outer cortical layers the course of the Fungus is somewhat 
irregular, both horizontally and vertically running hyphae being met with. 
On the whole, however, the mycelium seems to grow along the mycorhiza 
just as Janse (’ 97 ) observed in many of the roots which he investigated. 
Plate XIX, Fig. 1, which is a portion of the transverse section represented 
on Plate XVIII, shows the majority of the hyphae cut more or less trans- 
versely, and also exhibits them running, as they seem generally to do, 
close along the inner face of the cell-walls. This is often found to be 
the case in the living mycorhizae, where, however, the Fungus often forms 
more or less definite coils on the inside of the cell-walls. From these 
thicker coiled hyphae very thin haustorial filaments are sent into the 
