Nature Bulletin No. 330-A   February 1, 1969
Forest Preserve District of Cook County
George W. Dunne, President
Roland F. Eisenbeis, Supt. of Conservation

****:PLANTS OF THE COAL AGE

IN the preceding bulletin we told about the early part of the Age of 
Ferns when there were many low-growing kinds as well as the tree 
ferns, some of which were quite tall, with typical fronds and crowns of 
all sizes and shapes, but all reproducing by means of spores -- just as 
ferns do nowadays. In addition, the Seed "Ferns" appeared: the first 
plants that ever spread pollen or bore seeds. In appearance, except for 
primitive pollen sacs and seed sacs, they resembled the other ferns.

The Age of Ferns included what is known as the Pennsylvanian Period 
which began about 250 million years ago and lasted for some 35 million 
years. This was the first of two periods in the earth's history when 
luxuriant tropical vegetation blanketed the land from pole to pole and 
there were enormous accumulations of plant material which later 
became coal. The climate all over the earth, apparently, was very warm 
and humid with no seasonal changes. In addition to the ferns, tree ferns 
and seed ferns, there were giant club mosses as much as 100 feet tall 
with trunks three or four feet in diameter, treelike horsetails, and a new 
type of plant distantly related to our evergreen conifers: large trees that 
bristled with enormous needles like sharp green swords. The first 
mosses and liverworts also appeared. The vegetation was all green, 
yellow or brown. There were no flowers, no birds, no butterflies or 
bees. There were cockroaches, gigantic dragonflies and small reptiles 
but the world must have been strangely silent. It was during this period, 
the Coal Age, when the greatest deposits of plant material were made, 
which eventually were transformed into beds of bituminous and 
anthracite coal that circle the northern hemisphere from near the North 
Pole to the South Temperate Zone.

Then the earth's climate changed and there were serious disturbances of 
the earth's crust. The southern hemisphere was covered probably six 
times by glaciers advancing from the South Pole and, for the first time 
plants had to retreat. Some managed to "migrate" toward the equator 
and then returned toward their former ranges as the glaciers melted 
back, but some became extinct. The tree ferns, giant club mosses, and 
the tall horsetails all disappeared. Only the smaller hardier forms of 
ferns and horsetails survived. Then the climate became much drier all 
over the earth. Two new groups of plants developed: the first conifers 
and the cycads. The Age of Ferns, which has lasted almost since the 
dawn of plant life on land, was ended. For the next 95 million years or 
so, the vegetable kingdom had a new ruler.

The Age of Cycads, although it produced coal beds throughout the 
earth, was dominated by scrub forests because it was not so moist. Even 
the conifers, destined to be the world's tallest and biggest trees, seldom 
reached 60 feet in height. The Petrified Forest in Arizona consists of 
fossilized pines that grew in the Triassic Period. The cycads had woody 
stems or trunks that almost never branched, and crowns of palmlike or 
fernlike leaves at the top. The stems of some kinds were ringed by the 
remains of old crowns that died down to become new additions to the 
trunk, and they grew to be 50 or 60 feet tall. Many odd dwarf kinds 
covered the ground. One had a trunk only two feet high and just as 
wide. Leaves and fruiting bodies projected everywhere from its bark, so 
that its fossils look like overgrown honeycombs. There are still two 
small species of cycads native in Florida, and six in Mexico. In the 
Jurassic Period which followed, two important developments occurred 
in plants. The earth's climate was changing again.

Extra ! Extra ! Read all about it in the next bulletin.