404 MORPHOLOGY OF GYMNOSPERMS 



spermous), a fact apparent in the staminate "flower" of Welwitschia. 

 and made true for all other flowers of Gnetales by inferring the sup- 

 pression of one set of sporangia. The conspicuous illustration of a 

 proanthostrobilus among gymnosperms is of course found among 

 the Bennettitales. Based upon this strobilus situation, the Gnetales 

 are regarded as a phylum of gymnosperms having a common ancestry 

 with angiosperms, the two phyla in many particulars following parallel 

 lines of development. It hardly seems necessary to name hypotheti- 

 cal groups, but these common bisporangiate ancestors have been 

 called "hemiangiosperms." Thus the Gnetales have not given rise 

 to the angiosperms; and yet the resemblances of the two are satisfied 

 by the parallel development of two lines from a common ancestry. 

 The gymnosperm connection naturally involves the Bennettitales, 

 and all those groups whose monosporangiate condition may be the 

 result of the suppression of one set of sporangia. It is recognized 

 that in the evolution of strobili among gymnosperms there were prob- 

 ably two distinct tendencies : a monosporangiate strobilus (Cycadales, 

 Cordaitales, Ginkgoales, Coniferales), and a bisporangiate strobilus 

 with the anthostrobilus arrangement of sporophylls (Bennettitales, 

 Gnetales, and leading to angiosperms). 



LITERATURE CITED 



1. Hooker, I. D., On Welwitschia, a new genus of Gnetaceae. Trans. Linn. 

 Soc. London 24:1-48. ph. 1-4. 1863. 



2. EicHLER, A. W., Ueber Welwitschia mirabilis, etc. Flora 47:459-464, 

 473-479. 489-496, 508-510, 513-520. 1863. 



20. Watson, Sereno, Botany of King's Exp. 1871. 



3. Strasburger, E., Die Coniferen und die Gnetaceen. 1872. 



4. Beccari, O., Delia organogenia del fiori feminei del Gnetum Gnemon L. 



Nuovo Giom. Bot. Ital. 7:91-99. 1877. 



5. Strasburger, E., Die Angiospermen und die Gymnospermen. 1879. 



6. Bower, F. O., On the germination and histology of the seedlings of Wel- 

 witschia mirabilis. Quart. lour. Micr. Sci. 21:15-30. pis. j, 4. 1881. 



7. , On the further development of Welwitschia mirabilis. Quart. Jour. 



Micr. Sci. 21:571-594. pis. 22, 2j. 1881. 



8. , The germination and embryology of Gnetum Gnemon. Quart. Jour. 



Micr. Sci. 22:278-298. pi. 25. 1882. 



9. Karsten, G., Beitrage zur Entwickelungsgeschichte der Gattung Gnetum 

 Bot. Zeit. 50:205-215, 221-231, 237-246. pis. 5, 6. 1892. 



