330 HICK AND CASH : AFFINITIES OF LEPIDODENDROX. 
ii. The inner parenchyma, on the other hand, of both genera 
is composed of tliin-walled elements. In Selagbiella 
the innermost portion is traversed by an air-cavity 
surrounding tlie vascular bundle, across whicli are 
stretched cellular filaments whose elements are disposed 
somewhat radially. A radial arrangement of the cells 
is very conspicuous at the inner periphery of trie inner 
parenchyma of LepkJodeiidrou se.laginoideii, and this, as 
well as the position immediately outside the vascular 
bundle, points to the homology of this layer with the 
lacunar tissue of Selagiiwlla. Some confirmation of 
this is found in the fact that the foliar bundles of Lepi- 
dodendron are surrounded by similar radially-arranged 
rows of cells, while tlie corresponding bundles of Selag'i- 
nella are enclosed by lacunar tissue. 
2. Difterences. 
i. The centre of the stem of Seldginella is occupied by a 
simple vasular bundle (whether others are present or 
not), the cross section of which is usually an elongated 
ellipse. That of Lepidodendrou, as already stated, is a 
compound bundle, with a circular transverse section. 
ii. The vascular bundle of Sdaginella has a phloem sheath, 
but nothing corresponding to this has yet been observed 
in Lepidodendrun. 
iii. The vascular bundle of Selaginella is surrounded by an 
air-cavity which is not present in Lppidodendrori. 
TaXONOMIC RELATIONSHIP OF LePIDODENDRON, LyCOPODIUM 
AND Selaginella. 
In adding a few sentences by way of conclusion on the 
*".axonomic relationships of these genera, it may be well to say at the 
outset, that we accept Williamson's view of the Lycopodiaceous 
affinities of Lepidodendron as one which now rests on a sound scien- 
tific basis. In other words we are satisfied that the place of Lepi- 
dodedron is somewhere in the group now^ termed Lycopodineae. But 
whether, in that group, it should stand nearer to Lucopodium than 
SelagineUa or vice versa, is not so certain. 
