4 CTCADACE^:. 



traversed either by a single midrib or by a number of equal and 

 parallel veins. There are, however, certain variations from the 

 familiar cycadean type, even, in some of the living genera. In 

 the South African genus Stangeria* originally described in 1835 

 as a fern, the pinnae possess a fern-like venation, forming a 

 strongly marked contrast to the usual Zamia or Cycas type. 

 AYriting of this plant in 1854, Smith 2 notes that the peculiar 

 character of the leaf segments renders untenable the criterion of 

 venation, usually relied upon in discriminating between fossil ferns 

 and cycads. Among fossil leaves there are various genera which 

 have been assigned to cycads or ferns according to the preference 

 of different authors. The well-known genus Nilssonia has been 

 placed by Schenk and others among the Filicina, but it is usually 

 referred to as an extinct member of the Cycadacea ; the widely 

 distributed Tccniopteris has been assigned to both ferns and cycads, 

 but it is generally regarded as a genus of fossil ferns. The genus 

 Dictyozamites 3 and numerous others might be cited as examples 

 of doubtful forms which cannot with any certainty be assigned 

 cither to the PteridopJiyta or Gymnosjaermee. 



In a recent work on the Coal-Measures of Gard, Grand'Eury * 

 includes certain leaf forms in the class of gymnosperms, but by 

 other writers these have usually been described as ferns. To settle 

 such doubtful cases as these, Bornemann 5 undertook a minute 

 comparative examination of the epidermal cells of recent ferns 

 and cycads, and found what he considered fairly safe guides 

 in the rectangular or wavy outlines of the epidermal cells of 

 the leaves of these two sets of plants. Schenk 6 has followed 

 Uornemann's example in making use of this anatomical character 

 in the case of carbonized epidermal tissues of doubtful fossil 

 leaves, but the fern-like wavy walls in the epidermal cells of 

 Stangeria leaves preclude any trustworthy reliance on such a 

 method of separating ferns and cycads. 



1 Hooker, Bot. Mag. PI. 5121, vol. xv. [3] 1859. Reference given, to 

 Kunze, etc. 



- Smith, p. 88. 

 3 Nathorst (1). 



* Graud'Eury (1), p. 301. 



5 Bornemann. 



6 Schenk (A. 1), Flor. foss. Grenz. Keup. Lias. 



