3. INTRODUCTION
The word fossil is derived from a Latin verb Fodere
which means “to dig”.
Fossils may be precisely defined as “the remains of
ancient plants and animals preserved in the rocks orancient plants and animals preserved in the rocks or
different layers of earth.”
The branch of science in which we study the plants of
past geological ages through the investigation of
fossils, is called “Palaebotany” .
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4. Horneophyton (Hornea lignieri)
Division = Psilophyta
Class = Psilophytopsida
Order = Psilophytales
Family = Rhyniaceae Family = Rhyniaceae
Genus = Rhynia (Kidston & Lang)
Geographical occurrence = Lower Devonion period
Geographical distribution = Mostly reported from
Rhynia chert bed of Scotland.
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5. Characteristic
features
Horneophyton lignieri
was described for the
first time by Kidston and
Lang (1920) from Rhynie
chert bed as Hornea
lignieri.lignieri.
According to ICBN, the
original generic name
Hornea was previously
occupied by a flowering
plant.
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Horneophyton :- External morphology
6. External morphology
The plant was approximately 6-8 inches (15-20 cm)
high.
The underground portion of the plant consists of a
series of bulbous, corm-like structures bearingseries of bulbous, corm-like structures bearing
numerous unicellular rhizoids.
The basal corm lacks any evidence of
vascularization and is made up of dark, thick-
walled parenchymatous cells.
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8. Reproductive organ of
Horneophyton
The sporangia are borne externally
at the apex some of the aerial
branches.
Each sporangium isEach sporangium is
dichotomously branched and may
have 2-4 lobes of varying length.
The sporangial lobes are
ellipsoidal cylindrical in shape
with truncated distal end.
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9. Dehiscence of sporangia took place through an
apical pore. Extending into the sporangial cavity is
a column of sterile tissue around which a
continuous layer of sporogenous tissue, composed
of trilete isospores, overarched a central columella.
The sporangium of Horneophyton is unique The sporangium of Horneophyton is unique
among all vascular plants, because it consists of a
branched fertile unit resulted from dichotomies of
the stem apex.
Moreover, each fertile lobe was produced by its
own apex and remained meristematic for an
extended period of time.
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10. Classification of Cladoxylon
Class = Cladoxylopsida
Order = Cladoxylales
Family = Cladoxylaceae Family = Cladoxylaceae
Genus = Cladoxylon
Cladoxylales is represented by the genus Cladoxylon
with about a dozen species from middle Devonian to
lower Carboniferous.
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11. External
morphology of
Cladoxylon
The stem of Cladoxylon,
upto 5 cm in diameter,
was dichotomously
branched and spirally
bore numerous small
(rarely over 2 cm) leaves(rarely over 2 cm) leaves
which were
dichotomously dissected
in one plane and showed
heterophylly.
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Cladoxylon :- External habit
12. Fertile leaves were
borne on some
upper branches.
These
dichotomouslydichotomously
dissected and bore
at the tips of the
dissections small
sporangia. They
were homosporous.
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Cladoxylon :- Fertile leaves
13. Anatomy of
Cladoxylon
A T. S. of the stem shows
a broad homogenous
cortex, the central area
of which was polystelic.
The steles were many
and narrow, oftenand narrow, often
sinuous. They contained
scalariform and pitted
tracheides and each
stele was surrounded by
a secondary xylem.
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Cladoxylon :- Anatomy of stem
14. References
Pteridophyta for degree students (multicolour edition)
College botany for degree students
www.slideshare.net
www.biologydiscussion.org www.biologydiscussion.org
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