134 G. R. Wieland — Cycadeoidean Flower-hxid Structure. 



which plants clothed the land and by megaphyllous and then 

 simple stem-growth raised their structures above the moist soil 

 into the air and sunlight. And it is there in that oldest forest 

 that after the direct evolution of stem, vascular and leaf struc- 

 tures the primitive strobilar crown was organized and a point 

 established where branching and sterilization could set in and 

 thus inaugurate that vast course of aerial flower and seed 

 growth evolution, which has gone on unceasingly since early 

 Devonic time.* 



It is hypothesized, therefore, that as the earliest forest types 

 gradually grew larger and finally reached the normal size of 

 forest trees the segregation of the sporophylls in special axes 

 became more and more pronounced. Thus arose the seed and 

 the flower. But, as yet, it is most difficult to discern more 

 closely modes of early floral origin. There is only much sug- 

 gestion of " unequal rates " of evolution. For example, 

 Lyginodendron, very ancient of type and still semi-procum- 

 bent, is characteristically gymnospermous in its seeds, but 

 remains Marattia-like in its sporophylls in strong contrast to 

 the much older Cordaites, so far as we know the first great 

 forest type to achieve microsporophyll reduction. 



But too few forms are as yet known to satisfactorily illus- 

 trate any hypothesis. Because of the difficulty of the study, 

 progress is being made in large part by restudy and revision. 

 At best it is a most difficult task to say the last word about the 

 best conserved fossils, and except in the isolated " coal balls," 

 the Paleozoic forms are doubly difficult of interpretation. Yet 

 a fund of notable facts has been brought to light in the past 



* So far, nearly all the general outlines of ancient plant life have quite 

 failed to take into account not only the great role played by early seaweeds, 

 but the extreme antiquity of gymnospermous seeds and woods of high organi- 

 zation and cosmopolitan distribution. In consequence, after the extremely 

 important position the early land plants and first forests are now seen to 

 occupy in any larger scheme of plant evolution it is far from a mere digres- 

 sion to here modify the outline of plant development in geologic time long 

 since given by Brongniart, as follows : 



I 



Eeign of Primitive Life } 

 (Hypothetic) \ 



II 



Reign of Algae 



III 



Eeign of Early Land Plants 



IV 



Reign of Gymnosperms 



V 



Reign of Acrogens 



VI 



Reign of Proangiosperms 



VII 



Reign of Angiosperms 



- Oldest Precambrian 



j Precambrian 

 / Cambrian 

 \ Ordovician (?) 

 ( Silurian 

 Devonian 

 j Carboniferous 

 / Permian 

 ( Triassic 

 I Jurassic 



Cretaceous 



Tertiary 



