434 SCIENCE PROGRESS. 



PTERIDOPHYTA. 



Class — Sphenophylle^e. 



Genus Sphenophyllum. — Brongniart 1828 (Sftkeno- 

 pkyllites, Bronguiart, 1822). Stems comparatively slender 

 ( 1 *5 to 1 5 mm. ?), articulated, usually somewhat swollen at the 

 nodes, and marked by more or less distinct ribs and grooves 

 which do not alternate at the nodes, occasionally a single 

 branch given off at a node. Leaves in verticils, usually the 

 leaves of each whorl are equal in size, but may be unequal, 1 

 in multiples of 3, 6, 9, 12, 18 or more. The leaves of 

 successive whorls superposed, not alternate ; varying in 

 form from cuneate, with narrow base and multinerved 

 lamina having an entire or toothed anterior margin, to 

 narrow linear uninerved forms, or with a deeply dissected 

 lamina having dichotomously branched segments. 



Stem monostelic, with a triarch triangular strand of 

 centripetally developed primary xylem, consisting of 

 reticulate, scalariform and spiral tracheae ; the protoxylem 

 elements being situated at the blunt corners of the xylem 

 strand, from the angles are given off the foliar bundles, either 

 one or two from each angle. 



Secondary xylem consists of radially disposed reticulately 

 pitted tracheae, developed from a cambium layer. Phloem of 

 thin walled tissue including sieve-pitted tube-like elements 

 and phloem parenchyma. Both xylem and phloem traversed 

 by medullary rays of parenchymatous cells. Cortex largely 

 composed of fairly thick walled cells ; and in older stems 

 cut off by the development of deep-seated periderm. 



Fructification in the form of long and narrow strobili, in 

 some cases reaching a length of 12 cm., and a diameter of 

 14 mm. A slender axis bearing whorls of numerous linear 

 lanceolate bracts fused basally into a coherent funnel-shaped 

 disc, bearing on its upper surface sporangiophores 2 and 



1 Zeiller (2), p. 675. 



2 The strobilus of S. trichomatosum, Stur, figured by Kidston, is de- 

 scribed as having sessile sporangia. On this point see Williamson and 

 Scott, p. 942. An examination of Kidston's specimen certainly conveys, 

 the idea of sporangia without stalks, but the evidence is not conclusive. 



