RELATIONSHIPS OF METASPERMAE. 603 



In such a region of high competition specific and ordinal char- 

 acters would have progressively appeared and the littoral re 

 gions of the Cretaceous ocean, both east and west, would have 

 been fringed with the more highly specialised types of plants . 

 But the interior would more probably have been occupied by 

 solid masses of coniferous, fern-like and club-moss-like plants. 

 The general physiognomy then of Cretaceous regions must have 

 been much more distinctly coniferous than that of Northern 

 Minnesota at the present time. The proximity of the fringe 

 of metaspermic plants to the beach or estuary formations in 

 which their remains are preserved as imprints in the Cretace- 

 ous sandstone together with the remoteness of the solid masses 

 of coniferous plants from the same formations is the reason for 

 the preponderance of the former as fossils. 



The Tertiary flora. In Tertiary times, however, the Meta- 

 spermae had gained much ground, although they were probably 

 not so prevalent as they are to-day, nor had the dispersion of 

 the older coniferous flora reached such an extent as under 

 modern conditions. During at least the Miocene period of the 

 Tertiary the temperate climate of the Arctic regions persisted, 

 and during this time a considerable mingling of plants took 

 place over the northern hemisphere so that the influence was felt 

 by the plant-populations even to the equator. Engler has in- 

 terestingly discussed this Tertiary migration, and, in his chart 

 illustrative of it, the principal lines are indicated. In the old 

 world the movement extended to Arabia and Abyssinia, by way 

 of the central Asian route. At this time the central Asian 

 region was occupied by a large lake and a chain of such great 

 lakes extended throughout a large portion of the middle Mis- 

 sissippi valley in North America. During this period the 

 western and eastern portions of the North American continent, 

 now connected by the land area which in great part replaced 

 the Mediterranean ocean of the Cretaceous, were affected by 

 immigrations from the northwest and the characters of the 

 Japanese-Chinese region and the upper North American were 

 doubtless more similar than they are to day. For example the 

 curious gingko tree now isolated in the Japanese-Chinese 

 region was distributed also over portions of Europe and Can- 

 ada. This Tertiary mingling had a profound effect upon the 

 development of monocotyledonous and archichlamydeous 

 types. In both groups many arborescent forms originated. 

 While to-day there is not a single monocotyledonous tree in 

 the region of the Minnesota valley, there were then, in adjacent 



