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- 
sperme 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 eqnator. 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 
