CYCADACE.S. 



alone we must necessarily expect to fall into error, but it is 

 important not to bind ourselves too closely to the more common 

 forms of cycadean fronds in endeavouring to determine the leaves 

 of extinct species. Seeing that the existing genera of cycads are 

 obviously but a few remnants of a once vigorous and numerous 

 family, we should not neglect the less known and more aberrant 

 forms of fronds in our comparisons of fossil and recent specimens. 



We are accustomed to include in the Cycadacece a large number 

 of Jurassic and Lower Cretaceous fronds which possess some more 

 or less close external resemblance to those of living species. That 

 such determinations are correct we have no absolute proof, but 

 can only trust to the distinctly cycadean form which the leaves 

 present. It is possible that among such Mesozoic genera there 

 are included some which should rather come under the head of 

 Bennettitea, a group of plants nearly allied to the true cycads, 

 but which possess certain peculiarities of structure of sufficient 

 importance to exclude them from the Cycadacece as at present 

 denned. Sihcified stems from the Upper Jurassic and Lower 

 Cretaceous rocks of England, France, Italy, America, and other 

 places, agree in anatomical structure with the stems of recent 

 cycads, but in organic connection with some of these fossil forms 

 there has been found a special type of inflorescence, showing a more 

 highly organized and specialized structure than is afforded by the 

 flowers of existing Cycadece or Zamiece. Our knowledge of the 

 vegetative and reproductive structures of Bennettites is mainly 

 due to the researches of Carruthers, 1 Solms-Laubach, 3 and more 

 recently Lignier. 3 The Bennettitece inflorescence presents certain 

 points of contact with the Coniferce, and the characters it possesses 

 in common with and distinct from those of cycadean flowers 

 suggest that " the Bennettitece are posterior to the Cycadacece, at 

 least as regards the reproductive structures." As Lignier has said 

 in his recent paper, we may perhaps regard the Bennettitece as 

 a family which has been derived with the cycads from common 

 ancestors. We have still to learn what forms of frond were 

 possessed by these stems. Carruthers 4 speaks of a "remarkable 



1 Carruthers (1). 



2 Solms-Laubach (1 and 2). 



3 Lignier. (For abstract of this paper see Nature, October 18, 1894, p. 594.) 



4 Loe. cit. p. 697 (footnote). 



