Historical Foundation of Plant and Groundwater Interactions - Introduction to Phytoremediation of Contaminated Groundwater - page 10

leaves or location of growth. With his microscope, Linnaeus
observed that the number of stamen is constant for members
of the same kind of plant. This makes sense today, because
plants are parts of families that have similar genetic traits
that were unknown during Linnaeus' time. Also, these
features are less susceptible to changes induced by changes
in environmental conditions. He placed plants into 24 clas-
ses based on their differences in the sexual parts of each
plant.
That Linnaeus was corroborating his binomial classifica-
tion system with the notion that plants had separate sexes
was resisted and, in fact, considered by his peers to be
immoral. As a result, Linnaeus, against his wishes, had to
leave his teaching position at a university. In the end, it is the
binominal system that has stood the test of time rather than
the classification scheme based on sexual organs of plants.
This is because some plants that have the same number of
stamen are not related, and a constant number does not
indicate genetic relation.
At the time of his publication of Species Plantarum in
1753 (Linnaeus 1753), Linnaeus had named and classified
almost 6,000 species. This classification provided the basis
for later taxonomists to perform more accurate classifi-
cations. For comparative purposes, today upwards of
400,000 different species of plants, from the smallest photo-
synthetic microorganism to the tallest redwood tree, have
been classified according to Linnaeus' almost 260-year-old
system. Moreover, recent efforts to catalog all living things
on earth have reached over one million species. This number
and overall diversity would be higher if fossilized plants and
animals were included. The convention of using Latin names
still is being used today. Moreover, because the binomial
classification system is based on structural differences,
Linnaeus' system turned out to be congruent with the Theory
of Evolution offered later by Charles Darwin.
The classification of organisms was a topic of intense
scientific investigation by many scientists during the time
of Linnaeus. Another scientist in France also was
investigating the relation of various plants and animals to
one another. His name was Georges-Louis Leclerc
(1707-1788), perhaps more widely recognized by his title
Comte (Count) of Buffon, which was a small town in France
near his home. He wrote his observations of the natural
world into a large encyclopedia first published in 1749 called
Histoire Naturelle . As a contemporary of Linnaeus and
interested in answering similar questions about plant species
and organization, he did not accept Linnaeus' system of
plant classification based on the numbers of stamen and
pistils. Rather, Leclerc noticed that crossing two species
often resulted in sterile offspring, and that a species could
be defined as a group that produces fertile offspring. Even
though he published his topic 4 years ahead of Linnaeus, it
was the Linnaean system that survived, in part because the

Count's topic took more than 25 years for the translated
version to reach widespread readership in England.
Upon wide acceptance of the binomial system, it became
much easier for botanists to focus on other ways to study
similarities observed across various plants. Some of the
earliest studies by plant botanists involved solving the obvi-
ous problem of how plants take up and deliver water to
leaves at great heights above the land. These botanists pri-
marily focused on the structural components of plants that
are associated with water transport, for example, the xylem
and phloem tissues. Botanists also had to study perhaps the
most important part of the plant, especially in terms of its
relation to subsurface sources of water—the root system. In
many ways, it was this study of root interactions with water
that provides an early bridge between plant physiologists
and hydrologists. These investigations provide a firm foun-
dation of plant and groundwater interactions necessary to
support the later application of plants for the remediation of
contaminated groundwater.
The classification of plants has not been completed; it is
an ongoing occupation, carried out by plant experts known
as taxonomists. The task is the same as before: observe,
compare, classify, generalize, and specialize. As good as
the binomial nomenclature is as a classification system, it
remains an artificial system based on some actual relations
between genera of plants. It is not, however, a comprehen-
sive taxonomic endpoint—the natural system, which would
include all relations between all plant genera.

1.1.8 Plant Solute Uptake

After it was generally recognized that plants take up and
transport water from the soil and release it to the air as vapor,
scientists began to consider this process in the context of an
adaptation for plant survival and reproduction. As early as
1676, the scientist E. Mariotte, whom we will meet again in
Chap. 2, conducted experiments to demonstrate that the
uptake of water by plants provided a process for them to
obtain chemical elements from the earth. These experiments
were a logical step from the Humus Theory of Aristotle and
the experimental results of van Helmont. Advances in the
understanding of water uptake in plants were less dramatic
following Hales' work. In 1789, however, it is interesting
to note that Samuel Williams calculated that 3,874 gal
(gallons) (14,643 L [Liters]) of water passed through an
acre of maple trees per day (d) in Vermont, for an unreason-
ably high flow rate of 6 gal/day/tree (Williams 1789).
Plant research in the early 1800s focused not only on the
uptake of water but also of solutes. Remembering the exper-
iment of Johann Baptista van Helmont and his willow tree, it
was hypothesized that at least some minerals from the soil
dissolved in the water were taken up by plants. In 1804, the