316 MORPHOLOGY OF ANGIOSPERMS 



are a strictly monophyletic and modern group, since they possess 

 in common a very characteristic mode of arrangement of bun- 

 dles of a unique type, and since neither the structure of the 

 bundles nor their mode of disposition is palingenetic. Further, 

 the evidence of secondary growth in Gloriosa, etc., would seem 

 to indicate that the Monocotyledons have come off somewhere 

 from the Dicotyledons, which they resemble so closely in their 

 essential reproductive organs. This view of the matter seems 

 strengthened by the greater reduction of the sporogenous tissue 

 in the megasporangium of the Monocotyledons as compared 

 with the lower Dicotyledons, and by the entire absence of the 

 probably primitive phenomenon of chalazogamy, which is so 

 characteristic of the lower Dicotyledons. In the present state 

 of our knowledge we are apparently justified in considering 

 the Monocotyledons to be a modern, strictly monophyletic and 

 specialized group, derived from the Dicotyledons or their parent 

 stock, possibly by adaptation in the first instance to an amphibi- 

 ous mode of life.* 



LITEEATURE CITED 



1. METTENIUS, G. H. Beitrage zur Anatomie der Cycadeen. 1857. 



2. RENAULT, B. Cours de Botanique Fossile. Paris. 1880-1884. 



3. STRASBURGER, E. Histologische Beitrage. III. 1891. 



4. TIEGHEM, P. VAN. Traite de Botanique. Paris. 1891. 



5. CAMPBELL, D. H. Mosses and Ferns. New York. 1895. 



6. WILLIAMSON and SCOTT. Further Observations on the Organiza- 



tion of the Fossil Plants of the Coal-measures. Part. 3. Lygi- 

 nodendron and Heterangium. Phil. Trans. Roy. Soc. London 

 B. 186: 1896. 



7. SCOTT, D. H. The Anatomical Characters presented by the Ped- 



uncle of the Cycadaceae. Annals of Botany 11: 399-419. pis. 

 20-21. 1897. 



8. WORSDELL, W. C. On Transfusion Tissue ; its Origin and Func- 



tion in the Leaves of Gymnospermous Plants. Trans. Linn. 

 Soc. London Bot. II. 5 : 301-319. pis. 23-26. 1897. 



9. POTONIE, H. Metamorphose der Pflanzen im Lichte Palaeontolo- 



gischer Thatsachen. Berlin. 1898. 



10. JEFFREY, E. C. The Development, Structure, and Affinities of the 

 Genus Equisetum. Mem. Boston Soc. Nat. Hist 5: 155-190. 

 pis. 26-30. 1899. 



* It should be noted that the manuscript of Chapters XVI and XVII was 

 completed April 1, 1902. 



