The Present Position of Palaeozoic Botany. 149 



Triassic, while fairly uniform in its vegetative characters, presents 

 several different types of fructification, on which distinct genera will 

 no doubt eventually be founded. 



The habit of the plants is well known and characteristic. The 

 comparatively slender ribbed stem, not exceeding about a centimetre 

 in diameter, is articulated, and bears whorled leaves, the typical 

 number in each verticil being six. The leaves of successive whorls 

 are always superposed — an important character of the family, 

 whereas in the Equisetales alternating verticils are the rule. In the 

 forms originally described, on which the generic name was based, the 

 leaves are wedge-shaped, either entire, or slightly cut at the anterior 

 edge. In other forms of foliage, however, the leaves are deeply 

 divided, so much so that it becomes impossible to distinguish between 

 the segments and entire leaves. M. Z e i 1 1 e r has figured specimens of 

 SpJienophijIlum myriopJujUum with about 30 apparent leaves in a whorl, 

 no doubt due to the deep division of a smaller number. It frequently 

 happens, as in the well-known species S. cuneifoJium, that both forms 

 of foliage occur on the same plant, a character which suggested a 

 comparison with the Batrachian liammculi and the inference that 

 Sphenophyllum may itself have been an aquatic genus. The comparison, 

 however, does not hold good, for, as M. Zeiller has shown, the 

 deeply-divided foliage characterises the main stem, and the wedge- 

 shaped foliage the lateral vegetative branches, whatever their level, 

 while on the fruiting branches, which can scarcely have been sub- 

 merged, the narrow or deeply-cut leaves may occur. On anatomical 

 grounds, as we shall see below, it is highly improbable that SpJieno- 

 pkißlum was an aquatic. In certain forms, e. g., S. speciosum (once 

 separated under the generic name Trizygia), the leaves in the six- 

 leaved verticil are of unequal size, four being usually large and two 

 small; the small leaves are directed towards the same side throughout 

 the stem. The peculiarity is not constant, even in the same species, 

 but may be worth referring to, as it has been compared with the 

 heterophylly of the Filicinean genus Salvinia. 



The branching of Sphenophyllum has not yet been at all exhaus- 

 tively studied ; the branches were lateral, and solitary, springing from 

 the nodes, and probably placed between two leaves as in the Equise- 

 tales. 



The anatomical structure of Sphenophyllum. our knowledge of 

 which was first due to the researches of Renault in 1870, extended, 

 and in some respects corrected by those of Williamson (1874 — 1895), 

 is unlike that of any recent group of plants, though finding its nearest 

 parallel in the genus Psilofuni. The organization of the stem is al- 

 ways of the type termed by Jeffrey protostelic, i. e. there is a single, 



