158 THE GEOLOGICAL HISTORY OF PLANTS. 



cular scar, and situated in verticils at the top of well-marked nodes 

 of the stem. 



In tree-ferns the leaf -bases are large and usually without a dis- 

 tinct articulating surface. The vascular bundles are numerous. 

 Protopteris has rounded leaf-scars with a large horseshoe-shaped 

 bundle of vessels above and small bundles below. Caulopteris has 

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

 centrically. Palaeopteris,* 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 of Caulopteris, but the vascular bundles united 

 into a horseshoe-shaped band. 



2. Subdivision of Sigillarice in Accordance wiih their Markings. 



The following groups may be defined in this way ; but, being 

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

 from natural : 



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

 gniart, or S. Brounii, Dawson. Stem with broad ribs, usually much 

 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. Rhytidolepis, Sternberg. Type, S. scutellata, 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 possible that some of the smaller stems of this group 

 may be branches of trees of group first. 



3. Syringodendron, Sternberg. Type, S. organum, L. and H., 

 S. oculata, Brongniart. Stems ribbed; areoles small and round, 

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

 These are rare, and liable to be confounded with decorticated ex- 

 amples of other groups ; but I have some specimens which unques- 

 tionably represent the external surface. 



4. Fawlaria, Sternberg. Type, Sigillaria elegans of Brongni- 

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

 rows, but without distinct ribs, except in old or decorticated stems. 

 Fruit borne in verticils on the branches bearing transverse rows of 

 rounded scars. Leaves somewhat broad and longitudinally striate. 



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

 plied to the Devonian ferns of the genus Archceopteris. 



