362 Causes and Course of Organic Evolution 



it, are transitional in leaf and also — so far as accurately known 

 — in floral parts between cordaitals, araucarias, and the genus 

 Cunninghamia. From the Jurassic or lower cretaceous upward, 

 progenitors or representatives of the araucarioid, the spruce, 

 the pine, the redwood, and other pinaceous genera become 

 increasingly common, various cupressineous genera succeed 

 during the cretaceous and early tertiary, while Cupressus, 

 C'hamceq/paris, and Juniperus seem to have appeared last in 

 the early- and mid-tertiary periods. In stem and leaf modi- 

 fications, as in floral and fruit structure, the three last are 

 the most condensed, specialized, and evolved genera of the 

 series. Accordingly we have placed Cupressus and Juniperus at 

 the top of the coniferal line of ascent. 



That the more evolved coniferal genera such as Abies, Picea, 

 Pinus, Taxodium, Cupressus^ and Juniperus formed a dom- 

 inant evergreen group in northern temperate regions within 

 even historic times becomes evident, if we reflect on the enor- 

 mous areas in North America, Europe, and Asia that are still 

 covered by such forests, or that were covered "v^^tllin the past 

 10,000 years, and have been denuded by man. The manner 

 also in which they cover the ground, to the almost total exclu- 

 sion of other and especially herbaceous species, is a biologic 

 and ecologic feature of prime importance. 



There is left for consideration now the highest and most 

 completely dominant line of plant ascent, namely, that indi- 

 cated on the diagram (Fig. 13) as Protoangiospermia, which 

 leads up to and branches out into the great dicotyledonous 

 and monocotyledonous branches. 



But, before treating of these, the peculiar group of the Cas- 

 uarinales requires study, o^nng to its intimate relation, as 

 the writer believes, to Ephedra of the Gnetales, a view already 

 suggested by Engler {12Jt-: 18). As subsequently treated (p. 

 365) and as set forth in the diagram, the writer would view this 

 small unigeneric family as an offshoot and evolved product 

 from the Ephedracese, and so as comparatively remotely re- 

 lated to the main angiospermic line. The reasons for such 

 treatment are numerous and fundamental. Thus the bundle 

 structure and mode of growth of the stem are closely ahke; 

 the functioning of the stem and branches in place of the leaves 

 is similar; many and most suggestive resemblances are revealed 

 in the histology of the bundle tissues; the structure of the 



