CARBONIFEROUS LYCOPODS AND SPHENOPHYLLS. 131 



Sphenophyllum embraced " a peculiar group of plants which, 

 though standing close to the Lycopods, cannot be included 

 within them, but must be placed in a class by themselves — the 

 Sphenophylleoe" 1 Since that sentence was written much light 

 has been thrown on the structure of Sphenophyllum, especially in 

 regard to its fructification, and although the complete morphology 

 of the cone is not positively determined, still the evidence points 

 to the sporangium being a ventral lobe of the leaf. If this be 

 the true explanation, its morphology is quite different from that 

 of the sporangia of Lepidodendron, Sigillaria, or any of the 

 Lycopodiacece. 



Until the morphology of the fructification of Sphenophyllum is 

 definitely determined, it is, of course, impossible to fix the 

 systematic position of the genus, but, as far as one can judge at 

 present, it possesses a peculiar type of structure which stands out 

 free from all other groups, recent or fossil, with which we are 

 acquainted. 



To compare it with recent genera is not less difficult, nor is 

 there any clear data to proceed upon. The question has been 

 very fully gone into by the late Professor Williamson and Dr. 

 Scott, 2 and after a critical analysis of all the evidence available 

 for a comparison of Sphenophyllum with existing genera, the 

 conclusion they arrive at is — " We must be content for the 

 present to leave this remarkable genus in its isolated position, in 

 the hope that the extensive knowledge of its organization which 

 we possess may in the future afford an adequate basis for com- 

 parison when additional forms of Palaeozoic Cryptogams have 

 been brought to light." 3 They further say — " In fact, Spheno- 

 phyllum affords yet another example of a Carboniferous Crypto- 

 gam, which, so far from representing a primitive type, is in many 

 ways more elaborately modified than any recent forms;" 4 and 



1 Proc. Roy. Phys. Soc. Edin., Vol. XL, p. 61, PI. I. 1891. 



2 Williamson and Scott, " Further Observations on the Organisation of 

 the Fossil Plants of the Coal Measures— I.," Phil. Trans., Vol. CLXXXV. 

 (B.), p. 940, 1895; Scott, "On the Structure and Affinities of Fossil 

 Plants from the Palaeozoic Rocks," "On Cheirostrobus," Phil. Trans. , Vol. 

 CLXXXIX. (B.), p. 23, seq., 1897. 



3 Williamson and Scott, Phil. Trans., Vol. CLXXXV., p. 946. 1895. 



4 Williamson and Scott, I.e., p. 944. 



