428 



SCIENCE PROGRESS. 



his great work on Calamites, several specimens are figured 

 and described as evidence of the calamitean nature of 

 Sphenophyllum. A restoration of Calamites with spheno- 

 pylloid and other branches, given in his monograph, serves 

 to illustrate this view. 1 More recent investigation has, 

 however, conclusively proved that Brongniart's original 

 definition holds good. There can no longer be any doubt 

 that Sphenophyllum is a very well-defined generic type 

 holding a somewhat isolated position in the plant king- 

 dom. 



From structureless casts and impressions, we learn that 

 the genus is characterised by a comparatively slender 

 articulated stem bearing a series of superposed whorls of 

 leaves. The number of leaves in each verticil is always 

 some multiple of three, frequently six, or it may be nine, 

 twelve, eighteen, or more at each node. The leaves 

 have usually a wedge-shaped form, and the lamina is 

 traversed by dichotomously branched veins. In older forms, 

 again, the leaves are much narrower, and each segment in a 

 whorl has a single median vein. The narrow-leaved species, 

 such as Sphenophyllum myriophyllum Crep., etc., 2 cannot 

 always be readily distinguished from the well-known Astero- 

 'bhyllites form of foliage; but as Zeiller 3 points out, a careful 

 attention to the general habit of the plant, and the presence 

 of bifui cations in the leaves, should enable us to separate 

 these two generic forms. Another feature worthy of 

 note is the hetrophylly occasionally exhibited by this 

 genus. 4 The occurrence on the same plant of broad and 

 finely dissected leaves, naturally suggested to some authors 5 

 the idea of an aquatic plant ; but the histological features 

 are not such as are usually associated with water plants. 



Examples of Sphenophyllum met with in English Coal- 

 Measures do not, as a rule, attain any considerable length. 

 By far the longest stem which has come under my notice is 

 one in the Geological Survey Museum in Vienna ; in 

 this specimen there is an axis 4 mm. in breadth with a 

 length of 85 cm., giving off a slender branch 61 cm. in 



1 Stur, p. 69. 2 Zeiller (1), pi. lxii. 3 Zeiller (2), p. 674. 



4 Schenk, pi. xliv., fig. 1 ; Seward, p. 3, fig. 1. Etc. 5 E.g., Newberry. 



