TRANSACTIONS OF SECTION C. 347 



exhibit the transition from the younger or non-exogenous to the more advanced or 

 exogenous type. The cambium-layer has not developed throughout the entire cir- 

 cumference of the stem simultaneously, but has begun at one point, at the periphery 

 of the non-exogenous cylinder, from which point it has extended slowly right and 

 left, so as gradually to have crept round this inner vascular axis. In the specimens 

 referred to, this exogenous cylinder is incomplete, exhibiting a crescentic form, the 

 crescent being thickest at the centre, where the cambium-layer began to form, and 

 gradually becoming thinner as we approach the extremities of its two lateral 

 horns. This crescent, in different specimens, only embraces from one-third to two- 

 thirds of the circumference of the non-exogenous axis ; hence we have the anoma- 

 lous condition of a plant one side of which is a Sigillaria and the other a 

 Lepidodendron. Unless new features can be found other than what is often 

 designated the Diploxyloid condition of the vascular axis, whereby to distinguish 

 Sigillarise from Lepidodendra, the above-named distinction must obviously be 

 abandoned as having no'generic value. 



When a Lepidodendron was about to dichotomise, the vascular cylinder, as seen 

 in transverse sections, splits into two horseshoe-shaped halves. The author ex- 

 hibited specimens showing exactly the same conditions in a Sigillarian example. 

 The invariable dichotomisation is in itself a Lycopodiaceous feature. 



But one more remarkable fact is now demonstrated, which appears even yet 

 more conclusive. M. Van Tieghem has carefully shown that the idtiniate roots of 

 the Lycopodiacese and of the Ophioglossse have a structure which does not reappear 

 in any other portion of the vegetable kingdom. In the Cycadeae and Conifers, as 

 well as in the other vascular cryptogams, the centre of each root is occupied by a 

 cellular procambium enclosed within a pericambium or special cellular sheath. 

 From this sheath, at points located at measured distances and in varying numbers, 

 several, but never less than two, bundles of vessels are developed. The first 

 formed vessels are of small size ; but the more newly added ones increase in size as 

 each bundle develops centripetally, until their converging lines meet in the centre 

 of the procambium. But at the free ends of the peripheral portions of the roots, 

 in the case of the Lycopodiums, and throughout their entire length in the 

 Selaginellae, only one such procambial bundle makes its appearance. When per- 

 fected this bundle exhibits a triangular form in the transverse section — the apex of 

 the triangle, which always remains adherent to the pericambium, being occupied by 

 the small and first formed vessels, whilst its broad base, composed of larger vessels, 

 projects into the centre of the pericambium. These conditions reappear in the 

 most exact manner in the rootlets of the Stigmaria Jicoides, which all paleon- 

 tologists who know anything about the matter now admit to be the roots of 

 Sigillaria, as well as of Lepidodendron. This latter fact appears to the author, when 

 combined with the numerous other features which the plants have in common, and 

 with the absence of all real differences beyond such as are due to age, to be conclusive 

 of at least the ordinal unity of the Lepidodendra and the Sigillarise, and of the 

 Oryptogamic character of both. 



4. Evidence of the Existence of Palceolithic Man during the Glacial Period 

 in East Anglia. By S. B. J. Skertghlt, F.G.S. — See Section D, 

 Anthrop,, p. 379. 



5. The Geological Age of the Rocks of West Cornivall. 

 By J. H. Collins, F.G.S. 



The author had examined during some years the stratified rocks of West Cornwall 

 (marked as Devonian on the Government maps). 1 He discussed the determinations 



1 Some of the results of these observations have been already published. See 

 'The Hensbarrow Granite District,' Lake, Truro 1878, and Trans. Royal Geol. Soo. of 

 Cornwall, vol. ix. 1879. 



