XIl] CHEIEOSTROBUS 7 



It is clear that the types of strobilus designated Spheno- 

 phyllostachys (figs. 112 — 114) present a divergence of characters 

 too great to be comprised under one genus ; but in the absence 

 of fuller information, we cannot do otherwise than follow the 

 only logical custom of grouping them together as examples of 

 strobili borne by plants which, in the present state of our 

 knowledge, are most conveniently referred to the genus Spheno- 

 phyllum. 



Gheirostrohus. 



This generic name was applied by Dr Scott^ to a calcified 

 cone obtained by Mr James Bennie in 1883 from the Lower 

 Carboniferous plant-beds of Pettycur near Burntisland on the 

 Firth of Forth. Gheirostrohus is distinguished from Spheno- 

 phyllostachys by its greater breadth (3"5 cm.) ; externally it 

 agrees more closely with the fertile shoots of Lepidodendron 

 than with those of Sphenophyllum. A single vascular cylinder 

 having the form of a fluted Doric column (fig. 117, B, x) 

 occupies the axis of the cone : it consists for the most part of 

 reticulate tracheae which tend to assume a short or isodiametric 

 form in the central region ; the smaller protoxylem tracheids 

 with the spiral form of pitting constitute the sharp and 

 prominent ridges at the periphery of the xylem-cylinder. In 

 the outer part of the cylinder the metaxylem ^ consists exclu- 

 sively of tracheae, but towards the centre of the axis these are 

 associated with numerous parenchymatous cells. 



The xylem is therefore centripetal in origin as in Spheno- 

 phyllum and in nearly all recent and fossil members of the 

 Lycopodiales. In the type-specimen of Gheirostrohus the 

 vascular cylinder of the cone consists entirely of primary xylem, 

 but secondary xylem has been found in a more recently dis- 

 covered specimen*. Secondary xylem occurs also in the 

 peduncle of the cone. No appreciable remains of phloem have 



1 Scott (97) A. ; see also Scott (00) p. 106. 



' The term metaxylem may be conveniently applied to the primary xylem 

 other than protoxylem ; the latter is usually but by no means invariably 

 characterised by spiral thickening bands. 



3 Scott (05) p. 21 (footnote). 



