BENNETTITALES 89 



ment, all taken together present a combination of characters that 

 serves to set the group very distinctly apart from other gymnosperms, 

 and suggests that it represents the end of a gymnosperm phylum. 

 The testimony, on the whole, indicates that the Cycadofilicales 

 gave rise to at least two mesozoic phyla: one with monosporangiate 

 strobili, represented in the present flora by Cycadales; the other 

 with bisporangiate strobili, which culminated in the Bennettitales 

 and is probably not represented in the present flora. Whether there 

 was first a common stock from the Cycadofilicales, which later differ- 

 entiated into the two groups, or the two groups emerged from the 

 Cycadofilicales independently, is a question that can be discussed 

 rather than decided (27). 



LITERATURE CITED 



1. X/iNDLEY, J., and HuTTON, J., Fossil flora of Great Britain. 1830. 



2. Cakruthers, W., On gymnospermatous fruits from the secondary rocks 

 of Britain. Journal of Botany 5:1-21. 1867. 



3. Wn,LiAMSON, W. C, Contributions towards the history of Zamia gigas. 

 Trans. Linn. Soc. Bot. 26:663-674. pis. j2, 55. 1870. 



4. Caehuthers, W., On fossil cycadean stems from the secondary rocks of 

 Great Britain. Trans. Linn. Soc. Bot. 26:675-708. pis. 54-63. 1870. 



5. Solms-Laubach, H., Ueber die Fructification von Bennettites Gibsonianus 

 Carr. Bot. Zeit. 48:789-798, 805-815, 821-833, 843-847. pls.p, 10. 1890. 



6. , Fossil botany. English translation. Oxford. 1891. 



6a. PoTONi:^, H., Lehrbuch der Pflanzenpalaeontologie. Berlin. 1899. 



7. WiELAND, G. R., A study of some American fossil cycads. I. The male 

 flower of Cycadeoidea. Amer. Jour. Sci. IV. 7:223-226. pis. 2-4. 1899. 



8. , A study of some American fossil cycads. II. The leaf structure 



of Cycadeoidea. Amer. Jour. Sci. IV. 7:305-308. pi. y. 1899. 



9. , A study of some American fossil cycads. III. The female fructi- 

 fication of Cycadeoidea. Amer. Jour. Sci. IV. 7:383-391. pis. 8-10. 1899. 



10. Scott, D. H., Studies in fossil botany. London. 1900. 



11. Ward, Lester F., The Cretaceous formation of the Black Hills as indicated 

 by the fossil plants. 19th Annual Report U.S. Geol. Survey. 1900. 



12. , Description of a new genus and twenty new species of fossil cycadean 



trunks from the Jurassic of Wyoming. Proc. Wash. Acad. Sci. 1:253- 

 300. pis. 14-21. 1900. 



13. , Elaboration of the fossil cycads in the Yale Museum. Amer. Jour. 



Sci. IV. 10:327-345. pis. 2-4. 1900. 



14. WiELAND, G. R., The Yale collection of fossil cycads. Yale Sci. Monthly 

 6:1-11. pi. I. 1900. 



