Fossil plants, Vol. 3 : $b A text-book for students of botany and geologySeward, A. C. (Albert Charles)
Science
Fossil plants, Vol. 3 : $b A text-book for students of botany and geology
Seward, A. C. (Albert Charles)
Paleobotany
Certain problematical fossils found in association with the sterile
leaves of _Dolerophyllum Berthieri_ have been described by Renault as
the male organs of that species. These are elliptical discs, 6 × 5 cm.,
with an excentrically placed stalk: embedded in a carbonised lamina are
numerous rows of elliptical bodies, 410μ × 280μ, characterised by two
curved longitudinal grooves on the surface and regarded by Renault as
pollen-grains. The chains of these microspores radiate outwards from
the neighbourhood of the stalk and cover most of the surface of the
disc (fig. 432, B). Some silicified pieces of similar spore-bearing
discs from Grand’ Croix named _Dolerophyllum fertile_[390] afford
additional information as to these remarkable reproductive organs.
The earlier account of this species by Renault is confirmed by
Solms-Laubach[391] who examined the original sections. The peltate
fleshy discs preserved as incomplete specimens consist of lacunar
parenchyma 15–18 mm. thick traversed at right angles to the surface
by numerous loculi (fig. 432, C), circular or oval in transverse
section, containing large numbers of microspores, _s_, similar in size
and form to those on the carbonised discs of the Mt Pelé specimen.
Vascular strands occur between and parallel to the spore-chambers.
The spores contain 8–10 cells (fig. 432, D) and Renault believes that
dehiscence of the exine occurred along the two deep grooves which mark
the limits of an operculum. He emphasises the peculiar structure of
the microspores by speaking of them as prepollinia: in size and in
the presence of internal cells (? male prothallus) they resemble the
spores found in the pollen-chamber of a seed described by Renault as
_Aetheotesta elliptica_[392] which he thinks may belong to a member of
the Dolerophylleae. It has also been suggested that _Codonospermum_ may
be a seed of _Dolerophyllum_[393]. An unconvincing specimen described
by Saporta and Marion[394] as a seed-bearing bract is regarded by them
as referable to _Dolerophyllum_, but the evidence for any connexion is
far from satisfactory.
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