desert calendar - Desert Magazine of the Southwest

You can find all this in the flower of
the common white sage, Salvia apiana.
Well, after you have once become
acquainted with flowers and some of
their secrets, it's only natural to want
to know how they came to be here
in the first place. Most botanists incline
toward the classic theory that a
flower is a modified branch with whorls
of specialized leaves crowded together
in a definite order at the end of particular
stems. Several facts go to support
this view. For instance, the petals
of the common prickly pear grade
smoothly into sepals and it is practically
impossible to tell where petals
leave off and sepals begin. Others like
Indian Paintbrush, Castelleja, show
continuous grading from sepals to
green leaves like the foliage of the
stem. The fact that stamens in their
turn can grade into petals is shown
by Blazing Star, Mentzelia, where the
inner set of stamens are honest,
straight-forward stamens, but with
progression outward they become flatter
and flatter, lose their anthers and
finally become actual petals.
This evidence for continuous transition
of stamens to petals, petals to
sepals and from sepals to ordinary
leaves looks so critic-proof that it's
no shock when it is suggested that the
modern flower evolved from the spore
bearing leaves of some remote ancestor.
It is assumed that the leaves of this
flower-primeval grew like overlapping
scales around a central stalk and
formed a structure something like a
pine cone. Some scales are supposed
to have produced the pollen and some
the egg-cells.
According to this theory, the stalk
of this cone or strobile grew shorter
and shorter. The lower scales became
sterile and turned to petals while some
of the inner ones became elongated
and changed to stamens. The center
circle of scales grew together at the
edges to complete the rough sketch
of a modern flower with seeds enclosed
in a special capsule.
So far, the most that fossil plants
have shown to uphold this view is that
the extinct Lepidodendron tree of Carboniferous
time had cones that bore
egg-cells in the upper scales and pollen
in the lower. Unfortunately, this tree
is not an ancestor of any of our present
day flowering plants.
This classic theory of flower origin
from a strobile or conelet stood up
well for a long time. But in recent
years it has been pawed over by paleobotanists
loaded with new information.
A rigorous cross-examiner is Dr. Hamshaw
Thomas of Cambridge University
who points out some flaws in the
old theory that need explanation.
JULY, 1952
Fig. 2—Present-day blossom showing steps toward complete flower. No. 1
—catkin of the male willow; A—single staminate flower. No. 2—catkin
of female willow; B—single pistillate flower. In willows the sexes occur in
different plants. No. 3—flowers of alder, sexes are on adjoining stems; C—
male flowers; D—female. No. 4—flower shoot of castor bean, both sexes
on same shoot; E—male flowers; F—female; G—single male flower enlarged;
H—anthers; I—female flower, simply a capsule; J—style. No. 5—
single perfect but incomplete flower of Lizard's tail, a plant closely related
to Yerba Mansa; K—pistil; L—stamens. No. 6—perfect and complete
flower of geranium with all floral parts.
From a study of a long series of
fossil plants including the more recent
discoveries, Dr. Thomas suggests a
new possible lineage for our flowering
plants or angiosperms.
The first land plants were simple
types like Rhynia and a more recent
discovery from Australia called Baragwanathia.
These reproduced by means
of spores and were so simple in construction
you might call them unfinished.
The spores were not developed
in any special organ since the spore-
cases were simply the swollen ends of
the stems. Still later, some plants developed
special spore cases grown together
in pairs and the whole arrangement
supported by the flattened end of
the stem. These types had now reached
a point where they bear comparison
with male flowers of some modern
species.
These early plants may have favored
the "two household" or dioecious way
of life, pollen being produced on one
set of plants and seeds on another, an
arrangement still favored by the wil-
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