FBOM THE LOWEE COAL-MEASIJBES. 87 



single section shows all the details mentioned ; but nothing is 

 recorded which is not visible in one or more of them and is at 

 least consistent with the less definite structure of the rest. A 

 prolonged study of the sections has led to the conviction that the 

 specimen is a fragment of some Carboniferous plant which differs 

 in important points from anything that has been previously 

 described. It may represent a developmental stage of one of 

 the forms already known; but there is no evidence of this at 

 present, and hence it must stand apart, at least provisionally. 



General Structure. 



The general structure of the specimen, as indicated by the 

 transverse and longitudinal sections, is as follows : 



1. The centre is occupied by a cellular pith whose diameter is 

 about 2 \ centimetres. Prom all the characters it presents, this 

 appears to be a true pith, and not merely the central part of an 

 axile vascular strand which has remained parenchymatous. 



(PI. XVI. fig. 2 ; PI. XVII. figs. 3, 4, p.) 



2. Surrounding the pith is a ring of primary vascular bundles 

 of the collateral type. They vary in breadth tangentially, the 

 broader ones suggesting by their appearance that they have been 

 formed by the lateral coalescence of narrower ones (PI. XVII. 

 figs. 3, vb). At certain points of the bundle-ring small bundles 

 have left it * on the external side, and are evidently passing off to 

 lateral appendages of some kind (PI. XVII. fig. 4, ab). Like the 

 bundles of the ring, these are collateral. The extreme diameter 

 of the bundle-ring is about 5 centimetres. 



3. Between the vascular bundles run the medullary rays 

 (figs. 3, 4, mr\ which are relatively broad bands of parenchyma. 

 The isolated bundles just mentioned as leaving the ring stand 



opposite to medullary rays (fig. 4). 



4. The ring of vascular bundles is enclosed by an extremely thick 

 mass of tissues, which may be provisionally spoken of as the enve- 

 loping tissues (Pl.XVI. fig. 2). Their structure is not uniform, ana 

 presents characters w r hich, compared with those found in the same 

 position in other coal-plants, are remarkable. The whole mass 

 is so thick that it brings up the total diameter of the ape- 



* Or are entering it. It is obviously immaterial which mode of expression 



used 



