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158 



TUE GEOLOGICAL HISTORY OF PLANTS. 



cularscar, and situated in verticils at the top of well-marked no leg 

 of thi; 'iin. 



In trcc-fcrns the leaf-bases are largo and usually withou„ a dis- 

 tinct articulating surf»«ie. The vascular l)undles are numerous. 

 Protopteris has round(!d leaf-scars with a large hf)rseshoc- haped 

 bundle of vessels above and sniuU bundles l)olow. Oaulopteris has 

 large elliptic or oval leaf-scars with vascular scars disposed con- 

 centrically. Pal^opteris,* of Geinitz, has the leaf-scars transversely 

 oval and the vascular bundles confluent in a transverse band with an 

 appendage or outlying bundle below. Stemmatopteris has leaf- 

 scars similar to those oi Cauloptcris, but the vascular bundles united 

 into a horseshoe-shaped band. 



2. Subdii'iHion of Sicjillarim in Accordance with their Marldngs. 



The following groups maybe defined in this way; but, being 

 based on one cluiracter only, they are of course in all probability far 

 from natural : ' ■ 



1. Siyillarin, Brongniart. Type, Sigillaria reniformis, Bron- 

 gnijirt, or S. lirounii, Dawson. — Stem with broad ribs, usually mtu'h 

 broader than the usually oval or elliptical tripunctate areoles, but 

 disappearing at base, owing to expansion of the stem. Leaves nar- 

 row, long, three-nerved. 



2. RhytidolcpiH, Sternberg. Type, S. scuMlnta, Brongniart. — 

 Ribs narrow, and often transversely striate. Areoles large, hexag- 

 onal or shield-shaped, tripunctate. Leaves as in last group. Rings 

 of rounded scars on the stems and branches mark attachment of 

 fruit. It is i)ossibIe that some of the smaller stems of this group 

 niay be branches of trees of group first. 



3. Syrinjiodendron, Sternberg. Type, S. organnm, L. and IT., 

 S. oculala, Brongniart.. — Stems r* ' -^d ; areol»>s small and round, 

 and apparently with a single scar, ,, three closely approximated. 

 These are rare, and lial)l(! to l)e confounded with decorticated ex- 

 amines of other groups ; l)ut I have some specimens which unques- 

 tionably represent the external surface. 



4. Fdi'ulnria, Sternberg. Type. Sigillaria chgnns of Brongni- 

 art. — Leaf-bases hexagonal, or in young branches elliptical, in vertical 

 rows, but without distinct ribs, except in old or decor* icated stems. 

 Fruit borne in verticils on the nran<!hes l«'aring transverse rows of 

 rounded scars. Leaves somewhat broad and longitudmally .striate. 



* This name, preocciinied by Geinitz, has been inadvertently misap- 

 plied to the Dcvouiau ferae of the genuti ArcJueoptcris. 



