1885.]} Evolution in the Vegetable Kingdom. 751 
is one of the most striking facts revealed by paleontology. 
Heer’s Populus primeva, from the Urgonian of Pattorfik, Green- 
land, described ten years ago, still remains the sole representative 
of this sub-class in any formation below the Cenomanian and the 
most ancient dicotyledon known.’ Not less remarkable, however, 
has been the march of these plants since their earlfest manifesta- 
tion, as will presently be shown. 
Having thus noted the time of first appearance of each princi- 
pal type of vegetation, we may now hastily glance at the mode oi 
subsequent development of each. This might be done from two 
distinct points of view, the absolute and the relative, but as the 
former would be powerfully affected by the defects in the geolog- 
ical record, no attempt will be here made to represent it graphi- 
cally. The relative point of view, however, admits of such rep- 
resentation which in a’ certain respect eliminates these defects. 
Collectors of fossil plants do not seek specially for particular 
types. They take all they find, and hence if the chances of 
preservation are equal for all types the chances of finding 
plants of a particular type would depend upon its abundance 
in the flora of the epoch to be studied, while conversely, the 
degree to which any type of plants is represented in collections 
would be a fair measure of its abundance in the flora of the given 
epoch. The accompanying diagram is based upon this assump- 
tion, and clearly shows the progress of each of the leading 
pes. 
The facts sustain in a striking manner the early generalization 
of Brongniart, against which Dr. Lindley so strongly inveighed 
as late as 1836, that there has been a general upward tendency 
in structural development through the geological periods. The 
Silurian was the age of cellular cryptogams, consisting principally 
of marine Alge. The reign of the vascular cryptogams began 
with the Devonian and closed with the Permian, the ferns con- 
stantly taking the lead but being strongly supported by the Cala- 
mariz and Lepidophytes throughout the Carboniferous. The 
gymnosperms assumed supremacy in the Trias; the Cycada- 
* Fossil wood supposed to possess the dicotyledonous structure has several times 
been found in lower formations (see J. G. Kurr’s “ Beiträge zur fossilen Flora der 
Jura-formation Wiirttemberg,” Stuttgart, 1845, page 9; Sorby “ On the occurrence 
of non-gymnospermous exogenous wood in the Lias near Bristol,” Microsc. Soc, 
— Ill, 1852, pp. 91-92), but evidence of this class is not yet accepted as con- 
clusive. 
