388 BENNETTITALES [CH. 



description is based partly on the published accounts and in part 

 on an examination of sections in the British Museum, the Man- 

 chester University Museum, and in Dr Scott's collection. 



The elliptical form of the stem and vascular cylinder as seen 

 in transverse section, regarded by Carruthers 1 as a feature charac- 

 teristic of the genus, has no morphological significance and is in 

 part at least due to compression. In the large pith, the armour 

 of persistent petiole-bases separated by dense ramental scales 

 (fig. 517, A, B), and in habit, Cycadeoidea Gibsoniana agrees 

 generally with the stems of many recent Cycads', but the resem- 

 blance of the vegetative organs is in marked contrast to the 

 differences exhibited by the reproductive shoots. The pith con- 

 sists of parenchyma with scattered secretory ducts but no 

 medullary vascular bundles. In the pith of Cycadeoidea Peachiana 

 there are patches of tissue superficially resembling vascular strands, 

 but these are probably bands of internal phloem like those de- 

 scribed by Solms-Laubach 2 in some Italian stems. In none of 

 the English stems are there any clear indications of the occurrence 

 of more than one cambium in the stele. The secondary xylem 

 is entirely centrifugal with some smaller crushed elements, 

 presumably protoxylem, at the inner edge where the medullary 

 rays are especially broad. The xylem is of the manoxylic type 

 (fig. 518, A) as in recent Cycads ; though the medullary rays, 

 1 2 cells broad, are rather smaller than in recent species. The 

 tracheids are scalariform as in Stangeria (fig. 397). As in recent 

 Cycads there is a broad cylinder of secondary phloem (fig. 518, B) 3 

 composed of alternate layers of thick- walled and thinner elements 

 sieve-tubes and parenchyma : traces of lateral sieve-plates 

 occur on some of the elongated elements. Each leaf-trace arises 

 as a single strand from the lower edge of a mesh formed by the 

 large inner end of a medullary ray: on emerging into the inner 

 cortex the trace has the form of a U-shaped strand (fig. 519, A, U) 

 which passes direct to the petiole, following a steeply ascending 

 course in Cycadeoidea Saxbyana and almost horizontal in C. Gib- 

 soniana. Before entering the base of a leaf the trace breaks up 



1 Carruthers (70) Pis. LVH., LVIH. 



2 Capellini and Solms-Laubach (92) PI. v. fig. 2. 



3 See also Slopes (15) p. 47. 



