HARDWICKE'S SCIENCE-GOSSIP. 



177 



A genus of plants allied probably to Lepidodendron 

 is called Lycopodites, and is characterised by its 

 pinnated branches, with leaves inserted all round 

 the stems in two opposite rows, but not leaving well- 

 defined leaf-scars. Professor Williamson, as we have 

 observed, groups the Lepidodendra and Sigillaria 

 together with the Calamitese, as forming an exogenous 

 division of the vascular Cryptogams, whilst the ferns 

 form an endogenous division, " the former uniting the 

 cryptogams with the exogens through the Cycadeffi 

 and other gymnosperms, and the latter linking them 

 with the endogens through the Palmaceiv." 



Gyinnospernis. — Remains of coniferous trees are 

 tolerably abundant in coal from all quarters of the 

 earth ; some of these have been considered to have 

 been allied to the Araucarian pines, others again to 



Fig. 



122. — Fossil Coniferous Wood. Newcastle. 

 X 36 diam. 



Long. Sect. 



the yew family, but they chiefly differ from these in 

 having large piths. The fossil called Sternbergia has 

 been shown by Professor Williamson to have been 

 the cast of the hollow cavity formed by the shrinking 

 of the pith of some of these trees. The details of 

 structure of coniferous woods preserved in the 

 coal measures can be well seen with the aid of the 

 microscope, and the minutest structure, such as the 

 glandular discs, is clearly revealed. 



Whether any true Cycadecc have ever been found 

 in the Palaeozoic rocks is considered by Mr. Carruthers 

 to be doubtful. It should not be difficult to deter- 

 mine the question, as the Cycadean stem and fruit 

 have well-defined characters of their own. The trunks 

 are well marked by leaf-scars, the leaves are pinnated 

 in all the modern representatives save one, and have 



a single midrib, whilst the leaflets are marked by 

 fine parallel, and sometimes forked veins. The fruit 

 consists of nuts or seeds borne on scales, forming a 

 cone of a more simple structure than that of the 

 true Conifers. Some writers have considered that the 

 Cycads are represented in the coal measure by the 

 genera No3gerathia and Cycadites, and possibly also 

 by Psygmophyllum, and Cordaites ; clearer traces of 

 the early existence of this order of plants is found in 

 the overlying strata. 



Conifera. — Remains of Coniferous plants may be 

 very readily recognised by the peculiar structure of the 

 wood, this is characterised by the absence of dotted 

 ducts, and by the presence of glandular discs in the 

 walls of its fibres ; when these two characters occur 

 in conjunction, we may safely consider the specimen 

 under examination to be coniferous. 



The earliest conifers with which we are acquainted 

 are of an Araucarian type. The wood of this group 

 of plants is marked by an absence of resin canals, and 

 also differs from that of other conifers in the arrange- 

 ment of the discs on the cell-walls of the prosenchy- 

 matous tissue. These pores when they form a single 

 series are in contact, and form a straight line at the 

 point of contact, when in several rows they have a 

 spiral arrangement, and pressing upon each other 

 take a hexagonal shape. The chief representative of 

 the order, according to Schimper, in Carboniferous 

 times, is a genus called Araucarioxylon, Kr. , or 

 Dadoxylon, Endl., but Mr. Carruthers claims 

 Dadoxylon amongst the Taxoid conifers or yews. 



Some curious and well-preserved nuts have been 

 not unfrequently met with in the coal measures 

 whose relationship has not yet been absolutely 

 determined. Amongst these are some, which have 

 been grouped under the name of Cardiocarpon, which 

 may have been the fruit of the Dadoxylon. The 

 appearance presented by well-preserved specimens of 

 Cardiocarpon almost suggests the spikes of some 

 flowering plant, and they have in fact been described 

 as such under the name, Antholites. They have a 

 " stout stem with interrupted ridges bearing alternate 

 or nearly opposite bracts, more or less linear in form 

 and in the axils of these bracts are flower-like leaf- 

 bearing buds, from which proceed three or four linear 

 pedicels to which is attached the fruit ; this seems to 

 have been a flattish and somewhat heart-shaped 

 pericarp enclosing an ovate acute seed." * 



Another fruit is a nut named, from its conical ridged 

 shape, Trigonocarpon, which probably belonged to a 

 tree of the same order as the Cardiocarpon ; the fruit 

 of the Chinese genus Salisburia is said to resemble it 

 very closely. Sections of Trigonocarpon show that 

 it had four cellular integuments enclosing an albu- 

 minous interior which is now represented by calcic 

 carbonate ; the integument of the fossil is very thick 

 and, like that of the yew, may have been fleshy. The 



* Carriithers. 



