agree with that of Lycopodium in having only microspores. The size
of the two kinds of spores also singularly agrees in the two groups.
This is of some importance, for among the recent vascular Cryptogams
there is a remarkable uniformity in the size of the spores in the
members of the different groups, even when there is a great variety
in the size of the plants. Thus the spore of our humble wall-rue
is as large as that of the giant Alsophila of tropical regions. So
also the spores of Equisetum and Calamites agree in size, as may be
seen in woodcut 47, Figs. 3, 4, and 9, where the spores of the two
genera are magnified to the same extent. And a similar comparison
of the macrospore and microspore of Triplosporites with those of
Selaginella, and of the microspore of Lepidostrobus with that of
Lycopodium, exhibits a similar agreement. This is made apparent by
the drawings in woodcut 44 of the two kinds of spores of Selaginella,
3 and 4, with those of Triplosporites, 8 and 9, which are drawn to
the same scale."
The genus Sigillaria, as we have already said, has, according to the
observation of Hooker, small sporangia exactly agreeing in size and
form with those of Flemingites. Most probably the contents of these
small sporangia were the same in both genera, so that Sigillaria
would be placed with Flemingites and Lepidostrobus as arborescent
Lycopodiaceæ having their affinities with Lycopodium, as they have
all microspores only in their fructification.
The scales upon the Lepidodendron stems, as well as those in the
cones, are arranged in a spiral manner, in the same way as plants
of the present day. Professor Alexander Dickson has examined the
phyllotaxis of Lepidodendrons, and gives the following results of his
observations (Trans. Bot. Soc. Edin. xi. 145). The fossil remains
of Lepidodendrons are often so compressed that it is difficult,
or even impossible, to trace the secondary spirals round the
circumference of the stem. In those cases, however, where there is
comparatively little compression, _i.e._ where the stem is more or
less cylindrical, the determination of the phyllotaxis is easy. Of
such stems he has examined fifteen specimens, which may be classed
according to the series of spirals to which the leaf-arrangement
belongs:--
A. Ordinary series, ½, ⅓, ⅖, ⅜, 5/13, etc.
(a.) Single spirals (D turning to the right, S to the left).
(1.) _Lepidodendron_ (Possil Ironstone series). Stem about ¾
of an inch in diameter. Secondary spirals 8 D, 13 S, 21 D.
Divergence = 13/34 (or possibly 21/55).
(2.) _Lepidodendron_ (Knightswood, near Glasgow, Mr. J. Young).
Stem about 1½ inch in diameter. Secondary spirals 13 D, 21 S, 34
D. Divergence = 21/55.
(3.) _Lepidodendron_ (Possil Sandstone series). Trunk about
2 feet long, with an average diameter of 20 inches. Steepest
secondary spirals 55 S, 89 D. Divergence = 55/144.
(b.) Conjugate spirals.[11]
(4.) _Lepidostrobus ornatus_ (Bathgate coal-field). About ¾ of
an inch in diameter. Secondary spirals 10 D, 16 S, 26 D, 42 S.
Divergence = 13/(34×2) (Bijugate arrangement).
(5.) _Lepidostrobus_ (Plean, Stirlingshire, Mr. Mackenzie). About
½ an inch in diameter. Secondary spirals 9 S, 15 D, 24 S, 39 D.
Divergence = 8/(21×3) (Trijugate arrangement).
(6.) _Knorria taxina_ (from collection of Dr. Rankin, Carluke).
Somewhat compressed, 2-2½ inches[12] in diameter. Secondary
spirals 15 D, 24 S. Divergence = 15/(13×3) (Trijugate
arrangement).
(7.) _Lepidodendron_ (from Dr. Rankin's collection). About 1¼
inch in diameter. Secondary spirals 10 D, 15 S, 25 D, 40 S.
Divergence = 5/(13×5) (Quinquejugate arrangement).
(8.) _Lepidodendron_ (Dowanhill, Glasgow, Possil Sandstone
series). Trunk about 1 foot long, and 1 foot in diameter. The
upper portion exhibits secondary spirals 35 D, 56 S, 91 D; thus
indicating a 7-jugate arrangement, with divergence = 8/(21×7).
The arrangement on the middle and lower portion is indistinct
and confused; so much so as to render any determination of the
arrangement doubtful.
B. Series, ⅓, ¼, 2/7, 3/11, etc.
(9.) _Lepidodendron_ (Messrs Merry and Cunningham's Clayband
Iron-Pit, Carluke). Stem 2 inches in diameter. Secondary spirals
18 S, 29 D, 47 S. Divergence = 21/76.
C. Series, ¼, ⅕, 2/9, 3/14, etc.
(10.) _Lepidodendron_ (R. B. Garden, Edinburgh, Museum). Stem
somewhat flattened, 1-1½ inch in diameter. Secondary spirals 9 D,
14 S, 23 D, 37 S. Divergence = 13/60.
(11.) _Lepidodendron_ (Redhaugh, near Edinburgh, Mr. Peach). Stem
somewhat flattened, ¾ to ½ inch in diameter. Secondary spirals 9
S, 14 D, 23 S, 37 D. Divergence = 13/60.
D. Series, ⅕, ⅙, 2/11, 3/17, 5/28, etc.
(12.) _Knorria taxina_ (Stockbriggs, Lesmahagow,--Hunterian
Museum). About 1 inch in diameter. The specimen consists of a
main stem and one of the branches into which it has forked.
On the main stem the secondary spirals are 6 D, 11 S, 17 D.
Divergence = 5/28 (series, ⅕, ⅙, 2/11, 3/17, 5/28, etc.)--On the
branch the secondary spirals are 8 S, 13 D. Divergence = 8/21
(ordinary series, ½, ⅓, ⅖, ⅜, etc.)
E. Series, ½, ⅖, 3/7, 5/12, 8/19, 13/31, 21/50, etc.
(13.) _Lepidodendron_ (from Dr. Rankin's collection). About ⅞
inch in diameter. Secondary spirals 12 D, 19 S, 31 D. Divergence
= 21/50.
F. Series, ⅓, 3/10, 4/13, 7/23, 11/36, 18/59, etc.
(14.) _Lepidodendron elegans_ (Possil Ironstone). About 1¼ inch
in diameter. Secondary spirals 10 S, 13 D, 23 S, 36 D. Divergence
= 18/59.
(15.) _Lepidodendron_ (Possil Ironstone). About 2¼ inches in
diameter. Secondary spirals 23 S, 36 D, 59 S, 95 D. Divergence =
47/154.
From the above it is evident that the phyllotaxis of Lepidodendron
is extremely variable, as much so perhaps as that of those most
variable plants, in this respect, the Cacti. It is also clear that
what has been enunciated by Professor Haughton (Manual of Geology,
Lond. 1866, pp. 243, 245) as the law according to which the leaves of
palæozoic plants were arranged--viz. that of alternate whorls--does
not apply to these ancient Lycopods. Lepidodendron aculeatum is noted
by Naumann as exhibiting an 8/21 arrangement. (Poggendorff, Annalen,
1842, p. 5.) Professor Alexander Braun (Nov. Acta Ac. C. L. C. xv.
1, pp. 558-9), speaking of the excessive deviation from ordinary
arrangements in Equisetaceæ (including Calamites), compares them in
this respect with Lycopodiaceæ (including Lepidodendron), saying
that in these two families "the utmost limits of the domain of all
leaf-arrangement appears to be attained."
Lepidophyllum is certainly leaves of Lepidodendron, the different
Lepidophylla belonging to different species of the genus. The slender
terminal branches are noticed under the name of Lycopodites. In coal
from Fordel Mr. Daw has detected innumerable bodies (Plate III.
Figs. 1, 2, 3) which have been shown to be sporangia. (Balfour,
Trans. Roy. Soc. Ed. xxi. 187.) On their under surface Mr. Carruthers
has observed a triradiate ridge (Plate III. Fig. 4). (Geological
Magazine, 1865, vol. ii. p. 140.) These sporangia have been found
connected with the cone-like fructification called Flemingites, and
resembling Lycopodium (woodcut 44, Fig. 4). Many forms of fossil
plants, such as Halonia, Lepidophloios, Knorria, and Ulodendron,
belong to the Lepidodendron group. Knorria is said to be the internal
cast of a Lepidodendron.
Ulodendron minus and U. Taylori (Plate III. Fig. 11), found in
ferruginous shale in the Water of Leith, near Colinton, exhibit
beautiful sculptured scars, ranged rectilinearly along the stem.
The surface is covered with small, sharply relieved obovate scales,
most of them furnished with an apparent midrib, and with their edges
slightly turned up. The circular or oval scars of this genus are
probably impressions made by a rectilinear range of aerial roots
placed on either side. When decorticated, the stem is mottled over
with minute dottings arranged in a quincuncial manner, and its oval
scars are devoid of the ordinary sculpturings. Bothrodendron is a
decorticated condition of Ulodendron.
[Illustration: Fig. 45 _a_.]
[Illustration: Fig. 45 _b_.]
[Sidenote: Fig. 45. _a_, _Calamites Suckovii_, composed of jointed
striated fragments having a bark. Fig. 45. _b_, Septum or phragma of
a Calamite.]
Calamites (κάλαμος, a reed) is a reed-like fossil, having a
sub-cylindrical jointed stem (Fig. 45, _a_ and _b_; Fig. 46; Plate
IV. Fig. 4). The stem is often crushed and flattened, and was
originally hollow. Calamites is thus defined by Grand d'Eury (Ann.
Nat. Hist. ser. 4, vol. iv. p. 124):--Stem articulated, fistular, and
septate; outer part comparatively thin, formed of three concentric
zones--1, an exterior cortical layer now converted into coal; 2, a
thin subjacent zone of vascular tissue, now invariably destroyed;
3, a sort of inner lining epidermis, which is carbonified. Cortical
envelope marked interiorly with regular flutings, interrupted and
alternate at the articulations. Inner epidermis smooth, or scarcely
striated. Vascular cylinder thin; outer surface of bark more fully
fluted and articulated than the inner surface.
[Illustration: Fig. 46.]
[Sidenote: Fig. 46. Vertical stems of fossil trees, Calamites
chiefly, found in the coal-measures of Treuil, near Saint Etienne.]
Carruthers gives the following description of the structure of a
species of Calamite which he examined:--The stem was composed of a
central medulla, which disappeared with the growth of the plant,
surrounded by a woody cylinder, composed entirely of scalariform
vessels, and a thin cortical layer. The medulla penetrated the
woody cylinder by a series of regular wedges, which were continued,
as delicate laminæ of one or two cells in thickness, to the
cortical layer. The cells of those laminæ were not muriform; their
longest diameter was in the direction of the axis. The wedges were
continuous, and parallel between each node. As the axial appendages
were produced in whorls, the only interference with the regularity of
the tissues was by the passing out through the stem at the nodes of
the vascular bundles which supplied these appendages. As the leaves
of each whorl were (with one or two exceptions) opposite to the
interspaces of the whorls above and below, there was also at each
node a re-arrangement of the wedges of vascular and cellular tissues.
Schimper considers Calamites as having an analogy with Equisetum in
its fructification. He looks on them as fossil Equisetaceæ. Annularia
and Sphenophyllum are considered as establishing a passage from the
Equisetaceæ to the Lycopodiaceæ. Some gigantic fossil Equiseta had
a diameter of nearly 5 inches, and a height of 30 or more feet. The
branches, which adorned the higher part of them in the form of a
crown, are simple, and have at their extremity a spike of the size
of a pigeon's egg, and organised exactly like the spikes of living
Equiseta. The subterranean rhizomes are well developed, and gave
origin, like many Equiseta, to tubercles which had the form and size
of a hen's egg.
The characters of Equisetum of the present day and Calamites, are
exhibited in woodcut 47. They show a marked resemblance in the
fructification. (See also page 31.)
Plants of Calamites have been seen erect by Mr. Binney, and he has
determined that what were called leaves or branches by some are
in reality roots. Mr. Binney gives a full description of various
Calamites, under the name of Calamodendron commune, in his Memoir
published by the Palæontographical Society, 1868. There are between
50 and 60 species recorded.[13]
In Spitzbergen, in rocks of the Carboniferous epoch, there have been
found Calamites, Sigillaria, Lepidodendron, and ferns, apparently the
same as those found in the Carboniferous epoch in Europe--Calamites
radiatus, Lepidodendron Veltheimianum, Sigillaria distans, Stigmaria
ficoides. Some species--Sigillaria Malmgreni, Lepidodendron
Carneggiannum, and L. Wilkianum--seem to be peculiar to Bear Island.
[Illustration: Fig. 47.]
[Sidenote: Fig. 47. Fruits of Equisetum and Calamites. 1. _Equisetum
arvense_, L. 2. Portion of sporangium wall. 3, 4. Spores, with the
elaters free. 5. Longitudinal section of the part of one side of
cone. 6. Transverse section of cone. 7. _Calamites (Volkmannia)
Binneyi_, Carr., magnified three times. 8. Portion of the sporangium
wall. 9. Two spores. 10. Longitudinal section of the part of one side
of cone. 11. Transverse section of cone.]
According to Carruthers the Equisetaceæ are represented in Britain by
the two genera Calamites found in primary beds, and Equisetum found
in secondary rocks and living at the present day. The difference in
the structure of their fruits is shown in woodcut 47. The fruit of
Calamites, called Volkmannia Binneyi (woodcut 47, 7), is a small
slender cone composed of alternating whorls of imbricate scales,
twelve in each verticil. The scales completely conceal the leaves
connected with the fructification. The fruit-bearing leaves are
stalked, peltate, and are arranged in whorls of 6. There are four
sporangia borne on the under-surface of the peltate leaves. These
spore-cases have cellular parietes, and in their interior there is
a deposit of cellulose in the form of short truncate processes not
unlike imperfect spirals. The spores are spherical, and appear to
have thread-like processes proceeding from them, similar to elaters.
The fruit-cone bears a marked resemblance to the fruit of Equisetum
in its fruit-bearing leaves, sporangia, spores, and elaters (see
Figs. 18, 19, 20, 21). In the modern plant all the leaves of the cone
are fructiferous, while in the fossil plant some are fruit-bearing,
and others are like the ordinary leaves of the plant. It is thought
that the fossil may be reckoned as having a somewhat higher position
than that possessed by the living genus.
[Illustration: Fig. 48.]
[Sidenote: Fig. 48. Foliage and fruits of Calamites. 1 and 2.
Asterophyllites; 3 and 4. Annularia; 5 and 6. Sphenophyllum.]
The different forms of foliage called Asterophyllites, Sphenophyllum,
and Annularia, belong to the one genus Calamites, but they may form,
perhaps, well-characterised sections when their fruits are better
known. In woodcut 48 representations are given of the foliage and
fruit of varieties of Calamites. In 1 and 2 we see the simplest form
called Asterophyllites. The leaves are linear and slender, with a
single rib. The form called Annularia (3 and 4) differs chiefly
in having a larger amount of cellular tissue spread out on either
side of the midrib. This form has a different aspect in a fossil
state from the other, from its whorls of numerous broad leaves
spread out on the surface of deposition, while the acicular leaves
of Asterophyllites have penetrated the soft mud, and are generally
preserved in the position they originally occupied in reference
to the supporting branch. The third form (5 and 6) is called
Sphenophyllum, and consists of whorls of wedge-shaped leaves, with
one or more bifurcating veins. They occur like those of Annularia,
spread out on the surface of the shale.
[Illustration: Fig. 49-50.]
[Sidenote: Fig. 49. _Araucarioxylon Withami_, Krauss (_Pinites
Withami_), from the Coal-measures, Craigleith, near Edinburgh,
showing pleurenchyma with disks, and medullary rays. An excellent
specimen of a stem of this pine may be seen in the Edinburgh Royal
Botanic Garden.
Fig. 50. _Trigonocarpum olivæforme_, an ovate, acuminate,
three-ribbed, and striated fruit or seed, which some suppose to be a
sporangium of a Lepidodendron, others refer it to Cycadaceæ. Hooker
refers it to Coniferæ like Salisburia.]
True Exogenous trees exist in the coal-fields both of
England and Scotland, as at Lennel Braes and Allan Bank, in
Berwickshire; High-Heworth, Fellon, Gateshead, and Wideopen, near
Newcastle-upon-Tyne; and in quarries to the west of Durham; also in
Craigleith quarry, near Edinburgh, and in the quarry at Granton, now
under water. In the latter localities they lay diagonally athwart
the sandstone strata, at an angle of about 30°, with the thicker and
heavier part of their trunks below, like snags in the Mississippi.
From their direction we infer that they have been drifted by a stream
which has flowed from nearly north-east to south-west. At Granton,
one of the specimens exhibited roots. In other places the specimens
are portions of stems, one of them 6 feet in diameter by 61 feet in
length, and another 4 feet in diameter by 70 feet in length. These
Exogenous trees are Gymnosperms, having woody tissue like that of
Coniferæ. We see under the microscope punctated woody tissue, the
rows of disks being usually two, three, or more, and alternating.
They seem to be allied in these respects to Araucaria and Eutassa
(Fig. 61, p. 74) of the present flora. Araucarioxylon or Pinites
Withami (Fig. 49) is one of the species found in Craigleith quarry;
the concentric layers of the wood are obsolete; there are 2, 3, or
4 rows of disks on the wood, and 2-4 rows of small cells in the
medullary rays. Along with it there have also been found Dadoxylon
medullare, with inconspicuous zones, 2, 3, and 4 rows of disks, and
2-5 series of rows of cells in the rays. Pissadendron antiquum (Pitus
antiqua) having 4-5 series of cells in the medullary rays, and P.
primævum (Pitus primæva), with 10-15 series of cells in the medullary
rays, occur at Tweedmill and Lennel Braes in Berwickshire; Peuce
Withami (Fig. 1, p. 3) at Hilltop, near Durham, and at Craigleith.
Sternbergia is considered by Williamson as a Dadoxylon, with a
discoid pith like that seen now-a-days in the Walnut, Jasmine, and
Cecropia peltata, as well as in some species of Euphorbia.[14]
Sternbergia approximata is named by him Dadoxylon approximatum.
Hooker believes from the structure of Trigonocarpum (Fig. 50) that it
is a coniferous fruit nearly allied to Salisburia (Trans. Roy. Soc.
1854). Several species of Trigonocarpum occur in the Carboniferous
rocks, such as T. olivæforme from Bolton (Plate II. Fig. 5), and T.
sulcatum from Wardie, near Edinburgh (Plate II. Fig. 6). Noeggerathia
and a few other plants, such as Flabellaria and Artisia, are referred
by Brongniart to Cycadaceæ. Flabellaria borassifolia, according
to Peach, has leaves like Yucca. Noeggerathia has pinnate leaves,
cuneiform leaflets, sometimes fan-shaped; the veins arise from the
base of the leaflets, are equal in size, and either remain simple or
bifurcate, the nervation (venation) being similar to that of some
Zamias.
The fossils of this period, referred to as Antholithes,[15] have
just been shown by Mr. Carruthers to be the inflorescence of
Cardiocarpum (Geol. Mag. Feb. 1872), and he proposes to set aside
the former name, confining it to the tertiary fossils to which it
was originally given by Brongniart, and to use the latter name.
The main axis of the inflorescence is simple, stout, and marked
externally with interrupted ridges. The axis bears in a distichous
manner sub-opposite or alternate bracts of a linear-lanceolate
form and with decurrent bases. In the axils of the bracts were
developed flower-like leaf-bearing buds, and from them proceeded
three or four linear pedicels, which terminated upwards in a somewhat
enlarged trumpet-shaped apex. To this enlarged articulating surface
was attached the fruit, to which has been given the generic name
Cardiocarpum[16] (Fig. 51). The place of attachment is indicated by
the short straight line which separates the cordate lobes at the base
of the fruit. The fruit is flattish, broadly ovate, with a cordate
base and sub-acute apex. It consists of an outer pericarp, inclosing
an ovate-acute seed. That the pericarp was of some thickness,
and formed probably a sub-indurated rind, is shown by a specimen
preserved in the round, and figured (Fig. 53 _a_). The pericarp is
open at the apex; and the elongated tubular apex of the spermoderm
passes up to this opening. The seed forms a distinct swelling in the
centre of the fruit, and a slight ridge passes up the middle to the
base of the apical opening.
[Illustration: Fig. 51-52.]
[Sidenote: Fig. 51. _Cardiocarpum Lindleyi_, Carr. Fig. 52. Do.,
Coal-measures, Falkirk.]
These fossils are believed to be an extinct form of Gymnosperms. Two
species have been described, of both of which we are able to give
figures. The first figure is from the specimens collected by Mr.
Peach at Falkirk. It is Cardiocarpum Lindleyi (Figs. 51, 52); it has
a primary axis with sub-opposite axillary axes, bearing four to six
lanceolate leaves and three or four pedicels. Primary bracts short
and arcuate. Fruit ovate-cordate, with an acute bifid apex, and a
ridge passing up the middle of the fruit.
[Illustration: Fig. 53.]
[Sidenote: Fig. 53. _Cardiocarpum anomalum_ (Carr.), natural size:
with separate fruit (_a_), twice natural size--Coal-measures,
Coalbrookdale.]
The second species is Cardiocarpum anomalum (Fig. 53) from
Coalbrookdale; it has a primary axis with alternate or sub-opposite
axillary axes, slender and elongated, bearing many linear leaves, and
several slender pedicels; primary bracts long, slender, and straight;
fruits small, margined. The somewhat magnified separate fruit (_a_)
shows the thickness of the pericarp and the enclosed seed.
[Illustration: Fig. 54.]
[Sidenote: Fig. 54. _Pothocites Grantoni_, Paterson. _a_, Spike
natural size; _b_, Portion of spike magnified; _c_, Perianth,
4-cleft, magnified.]
In the bituminous shale at Granton, near Edinburgh, Dr. Robert
Paterson discovered in 1840 a peculiar fossil plant, which he called
Pothocites Grantoni (Fig. 54, _a_). It is figured in the Transactions
of the Edinburgh Botanical Society, vol. i. March 1840. It is a spike
covered by parallel rows of flowers (Fig. 54, _b_), each apparently
with a 4-cleft calyx (Fig. 54, _c_). It was supposed to be allied to
Potamogeton or Pothos, more probably to the latter. In that case it
must be referred to the natural order Araceæ. The original specimen
is deposited in the museum at the Royal Botanic Garden, Edinburgh.