Biology Reference
In-Depth Information
place in the realm of fern systematics, and after her paper, he launched into
a tirade against the misconceptions and misinformation being presented.
After several minutes he sat down breathing heavily while Hires stood qui-
etly in her own world at the podium until he had fi nished. Then she said to
him, “Mister, you come to my booth this afternoon and I'll straighten you
out.” Herb Wagner and everyone in the room enjoyed the moment.
The use of spores and pollen in vegetation history, like macrofossils, also
relies on comparative material from herbarium collections. The method is
based on several principles or generalizations. First, almost all plants pro-
duce either spores or pollen grains. This means that no major taxonomic or
ecological group is a priori excluded from the fossil record. The exceptions
are widely known and include some aquatics because of their thin exine
or pollen wall, as well as the important tropical plant family Lauraceae—
Ocotea
, 350 species in the neotropics;
Nectandra
, 120 species;
Persea
, 100
species. The chemistry of the exine in the Lauraceae precludes preserva-
tion of the pollen, but the leaves are common as fossils. With these excep-
tions, pollen from most kinds of plants can be incorporated into the fossil
record. It is estimated that the wind-pollinated spruce forests of southern
Sweden produce 75,000 tons of pollen each year that is distributed region-
ally and falls as the pollen and spore rain. Insect pollinated plants are com-
mon in the tropics, and they usually produce smaller amounts of pollen
that is large, heavy, sticky and less likely to be preserved. However, because
of higher rainfall in the tropics, this pollen is often transported into depo-
sitional basins by outwash, and it is commonly found in small amounts in
tropical microfossil fl oras.
Second, pollen and spores are capable of being fossilized because the
spore wall and the exine are extraordinarily resistant to acid conditions.
This means that sediments accumulating in stagnant, organic, low pH en-
vironments, such as peat bogs, lake bottoms, and swamps (and converted
to lacustrine shales, lignite, and coal) are often rich in plant microfossils.
A sample the size of a marble can yield 100,000 or more spores and pollen
grains representing 350 different kinds of plants. If samples are collected
from horizontal exposures extending over a long distance, and vertically
every several centimeters up a section (canyon walls, river or road cuts; see
fi g. 6.2) or from well cores (see fi g. 7.4), and compared with other fossil
fl oras from the region, an extensive inventory is available of the vegetation
and vegetation change over the landscape and through time. The resistance
of the wall is refl ected in the methods used to recover plant microfossils
from sediments. If a hammer, bicycle chain, pair of pliers, and pollen were
placed in a platinum crucible and warmed with hydrofl uoric acid for a
