200 Carruthers — On a Fossil Cycadean Stem. 



Brongn. Besides the two species described by Buckland, from the 

 isle of Portland, the genus contains a third species from the Lias of 

 Lyme Eegis, also having, like the original species, a bulbiform trunk, 

 and three species with cylindrical stems from Secondary strata in 

 France. All the species are characterised by having their trunks 

 covered with the persistent bases of the petioles. With Professor 

 Morris's concurrence I have named the species .Cycadoidea Yatesii, 

 after a gentleman whose name is well known, among other things, as 

 a successful cidtivator and diligent student of the interesting Order 

 of plants to which the fossil belongs. I do not hesitate to give it a 

 specific name, as the materials are more than suificient to show its 

 affinities ; and though other vegetable fossils are known from the bed, 

 none have been described to which this could belong. 



The species may be thus distinguished : — 



Trunk cylindrical, covered with the persistent bases of the petioles, 

 which are rhomboidal in form, and terminate in a tumid boss, the 

 apex of which is directed upwards. 



The fossil belonged to an arborescent Cycad resembling in aspect 

 the tall cylindrical stems of Cycas or Macrozamia, and differed in this 

 respect from the spherical or ovoid trutiks belonging to the genus, 

 which were described by Buckland and Lindley. The cellular axis 

 was relatively very large. The pith has disappeared, except in one of 

 the specimens, where there are still some indications of it, and of the 

 vascular bundles which abounded in it. The woody cylinder surround- 

 ing the pith consists of two rings, everywhere pierced by medullary 

 rays, which are often so large as to separate the rings into numerous 

 series of woody wedges, as in recent Gycadece. The presence of discs 

 on the woody vessels has been detected both by Professor Morris and 

 myself. The inner surface of the woody cylinder is marked by 

 numerous narrow grooves and perforations, formed by the vascular 

 bundles, as they passed from the pith into the wood. The outer sur- 

 face has similar scars, produced by the vascular bundles, which passed 

 from the wood to the leaves ; but they are here larger and more regu- 

 larly disposed than on the inner surface. Between the wood and the 

 bases of the petioles there interposed a very thin layer of cellular tis- 

 &\\e, through which the vascular bundles passed in an upward direction 

 towards the petioles. In recent Cycadecs, as well as in the other fossil 

 British species of this genus, this layer is very much thicker than in 

 our species. The bases of the petioles rise from this cellular layer. 

 The leaves of Gycadece perish at first like the fronds of ferns and the 

 leaves of monocotyledonous plants, which not being articulated to 

 the stem of the supporting plant, wither and decay upon it. But a 

 true articulation exists in Cycads, not as in deciduous leaves at the 

 point where the base of the petiole rests on the surface of the stem, 

 but at some distance from that point. When the decayed leaf at 

 length falls ofi\, the cicatrix is covered by an epidermal layer, giving 

 to the persistent bases of the petioles an appearance not easily dis- 

 tinguished from the scales, which are interspersed among them. 

 Some species of the South African genus Encephalartos afford fine 

 • specimens of this structui-e, the outer surface of the trunk having 



