FLORIN: SYSTEMATICS OF THE GYMNOSPERMS 373 



trace the origin and evolution of the latter. There has been, to a considerable 

 extent, parallel and convergent evolution in the Cycadophyta and the Conifero- 

 phyta, and similar types of structure have originated in diverse groups at the 

 same or different times. The evaluation of characters or groups of characters for 

 taxonomic purposes sometimes varies considerably. Further progress in this 

 field appears to require not only continued and intensified accumulation of new 

 data, but also a new, unprejudiced analysis and synthesis of the implications 

 of all available facts. The possibility of increasing the efficacy of the methods of 

 approach applied to the study of the phylogeny of the gymnosperms is by no 

 means exhausted. In the last hundred years they have gradually allowed us to 

 acquire an immensely valuable insight into the main historical steps and events 

 of the evolutionary process. The edifice of phylogenetic classification, is, as 

 Sprague {in Huxley, 1940) wrote, subject to continual pulling down and re- 

 building, but many foundation stones remain in position, and the permanent 

 structure is steadily growing. 



BIBLIOGRAPHY I. 



Aase, H. C. 



1915. Vascular anatomy of the megasporophylls of conifers. Bot. Gaz., 60:277-313. 



Abbema, T. van 



1934. Das Transfusionsgewebe in den Blattern der Cycadinae, Ginkgoinae und Coni- 

 ferae. Rec. Trav. Bot. Neerl., 31:309-390. 



Allen, G. S. 



1946a. The origin of the microsporangium of Pseudotsuga. Bull. Torrey Club, 73:547- 

 556. 



1946b. Embryogeny and development of the apical meristems of Pseudotsuga. I. Fer- 

 tilization and early embryogeny. Amer. Journ. Bot., 33:666-677. 



Anderson, E. 



1937. Cytology in its relation to taxonomy. Bot. Rev., 3:335-350. 



Andersson, E. 



1947. A case of asyndesis in Picea Abies. Hereditas, 33:301-347. 



Andrews, H. N. 



1940. On the stelar anatomy of the pteridosperms, with particular reference to the 

 secondary wood. Ann. Mo. Bot. Gard., 27:51-118. 



1942. Contributions to our knowledge of American Carboniferous floras. I. Sclerop- 

 teris, gen. nov., Mesoxylon and Amyelon. Ann. Mo. Bot. Gard., 29:1-18. 



1945. Contributions to our knowledge of American Carboniferous floras. VII. Some 

 pteridosperm stems from Iowa. Ann. Mo. Bot. Gard., 32:323-360. 



1948. Some evolutionary trends in the pteridosperms. Bot. Gaz., 110:13-31. 

 Arber, a. 



1950. The Natural Philosophy of Plant Form, xiv + 247 pp. Cambridge: Cambridge 

 Univ. Press. 



Arnold, C. A. 



1930. The genus Callixylon from the Upper Devonian of central and western New 

 York. Pap. Mich. Acad., 11:1-50. 



1938-1948. Palaeozoic seeds. I-II. Bot. Rev., 4:205-234; 14:450-472. 



1947. An Introduction to Paleobotany, xi + 433 pp. New York and London: McGraw- 



Hill. 



1948. Classification of gymnosperms from the viewpoint of paleobotany. Bot. Gaz., 



110:2-12. 



