CYCADOPHYTA.
The term Cycadophyta, suggested by Nathorst[1069], is used in a
comprehensive sense to include both recent Cycads and the much
larger number of extinct types which it is customary to speak of
as Cycadean plants or fossil Cycads. The designation ‘Cycads’ in
the case of the majority of the fossil forms is, however, open to
criticism on the ground that they differ too widely from existing
genera to be associated with them in one class. It would be pedantic
and inconvenient to give up the almost universal practice of extending
the term Cycad beyond the limits defined by the characters of
recent species. The important point is to adopt some classification
which gives expression to our views as to the degree of affinity
between recent and extinct types. In a considerable number of cases,
especially impressions of presumably Cycadean fronds and stems that
occur without any fertile shoots, it is impossible to determine the
degree of relationship to modern types. It was with a view to a
rational group-designation for such fossils that Nathorst proposed
the term Cycadophyta, including in it the two classes Cycadales and
Bennettitales. The Cycadales comprise the recent genera and such
extinct types as may legitimately be included in the same class, but
as we shall see later there are hardly any fossil species that can be
assigned to this section on thoroughly satisfactory grounds. The term
Bennettitales is used by Engler, Nathorst, and several other authors as
a class-designation for a large number of Mesozoic Cycads agreeing in
their more important morphological characters with the Lower Cretaceous
stems on which Carruthers[1070] founded the genus _Bennettites_,
placing it in a new tribe, the Bennettiteae. Some authors have followed
Carruthers in the use of the family-name Bennettiteae for a subdivision
of the Cycadales equal in rank to the Cycadaceae, while others, wishing
to give greater emphasis to the difference between the extinct and
recent plants, prefer to adopt the class-name Bennettitales. Carruthers
regarded _Bennettites_ as occupying the same position in relation to
other Cycads as _Taxus_ holds with regard to the cone-bearing members
of the Coniferae. The adoption of Bennettitales is intended to convey
the impression that the class is more distantly related to the recent
Cycads than is implied by the analogy of _Taxus_. Nathorst[1071], as
the result of his discovery of certain reproductive organs associated
with some Rhaetic fronds described as _Dioonites spectabilis_, proposed
a third subdivision, the Dioonitales, but he subsequently[1072]
restored the fronds to their original designation _Nilssonia
pterophylloides_, and on further examination found that the supposed
microspore-bearing organs were seeds. _Nilssonia pterophylloides_
would therefore find a more natural place in the class Nilssoniales
instituted by Thomas[1073].
BENNETTITALES.
=Cycadeoidea.= Buckland.
In 1827 Buckland[1074] proposed the generic name _Cycadeoidea_ for
some petrified stems from the Purbeck beds in the Isle of Portland and
published a description of two species, _Cycadeoidea megalophylla_
and _C. microphylla_. Brongniart[1075] considered Buckland’s term
_Cycadeoidea_ inappropriate and proposed in its place _Mantellia_, the
type-species being _Mantellia nidiformis_ Brongn., the Portland stem
which Buckland a month or two later called independently _Cycadeoidea
megalophylla_. Subsequently Brongniart[1076] withdrew _Mantellia_ as
it had been previously used by Parkinson for a sponge and substituted
_Cycadites_. Some years later Carruthers[1077] revived _Mantellia_
for a type of Cycadean stem from Portland though one species,
apparently indistinguishable from those referred to _Mantellia_, he
named _Bennettites portlandicus_. There is no adequate reason for the
retention of the generic name _Mantellia_. The close resemblance of the
short and thick stems (12–30 cm. in height) described by Buckland to
those of some recent Cycads was recognised by Robert Brown and Loddiges
and the former suggested to Buckland the inclusion of the fossils in
a new family Cycadeoideae. It was this suggestion that led Buckland
to adopt _Cycadeoidea_ as a generic name. In a later account of the
Portland stems Buckland[1078], in deference to Brongniart’s opinion,
substituted Brongniart’s name _Cycadites_ for _Cycadeoidea_. It is
noteworthy that no reference is made in the original description to
the occurrence of lateral shoots among the persistent petiole-bases
that encase the Portland stems, but in a later account such shoots
are represented in one of the figured stems and are compared with the
buds occasionally produced on stems of _Cycas_[1079]. The subsequent
researches of Carruthers[1080] demonstrated the reproductive nature
of precisely similar lateral shoots in the stem on which he founded
the genus _Bennettites_. The generic name _Echinostipes_ given by
Pomel[1081], who had a passion for instituting new nomenclature, to
Buckland’s Portland stems has not been adopted: his genus _Crossozamia_
proposed for certain stems and fronds was revived by Carruthers[1082]
but has not been generally used. A further complication in the
nomenclature of Cycadean stems was introduced by Saporta’s
institution[1083] of _Bulbopodium_ and _Cylindropodium_: in the former
genus he included the small ovoid stem figured by Lindley and Hutton
as _Cycadeoidea pygmaea_[1084] and two French Jurassic species which
might reasonably be assigned to _Cycadeoidea_. To _Cylindropodium_ were
referred some large French stems from Jurassic strata: an examination
of the type-specimens in Paris convinced me that they are typical
forms of _Cycadeoidea_. As Ward[1085] has pointed out, both Saporta’s
genera may be merged in _Cycadeoidea_. Fliche and Zeiller[1086] also
include the small globular stems named by Saporta _Bulbopodium_ in
the older genus _Cycadeoidea_: one such type from the Portlandian of
Boulogne is described by these authors as _Cycadeoidea pumila_. Saporta
also proposed the name _Platylepis_[1087], the type-species being
_Cycadeoidea micromyela_ Mor., from the Lias of Calvados, which has
recently been investigated by Lignier[1088] who wisely adopts Morière’s
designation. Another unnecessary generic name is _Schizopodium_ given
by Morière to a stem, _S. Renaulti_[1089], regarded by Lignier as
indistinguishable specifically from _C. micromyela_.
The two names _Cycadeoidea_ and _Bennettites_ have been used by
authors for stems which are unquestionably generically identical
and as is often the case much confusion has been caused through the
failure of palaeobotanists to arrive at an agreement. Lester Ward, a
staunch advocate of the rule of priority, repeatedly pointed out that
Buckland’s name _Cycadeoidea_ should take precedence of _Bennettites_
on the ground that stems for which these genera were instituted are
clearly of the same type, and he added that the older genus, though
abandoned by its author, cannot be given up without violating the
inexorable rules of priority. On the other hand it has been urged that
the genus _Bennettites_ as defined by Carruthers is characterised
by the possession of (i) fertile shoots bearing strobili and (ii)
vegetative organs exhibiting certain anatomical characters. Buckland’s
species of _Cycadeoidea_, though bearing lateral shoots, are not well
enough preserved to afford definite information as to the morphological
features of the strobili, nor have we satisfactory data with regard
to the degree of resemblance between the vegetative features of
_Bennettites_ and the Portland stems. Carruthers laid stress on the
elliptical section of the stele in _Bennettites_ in contrast to the
cylindrical cylinder of Buckland’s _Cycadeoidea_ trunks. Subsequent
research has shown that this difference is not in itself a valid
criterion either of generic or specific rank but, as Wieland says, it
is an open question to what extent the stem structure of _Cycadeoidea_
and _Bennettites_ agrees. The probability is that were our knowledge
of the Portland stems less incomplete, they would be found to possess
no anatomical features inconsistent with this generic union. Granting
the correctness of this view, the adoption of the later generic term
would be a reasonable course to follow on the ground that it stands
for stems showing well preserved structure, while _Cycadeoidea_ was in
the first instance applied to stems showing only partially preserved
stumps of strobili, and the name was not retained by its author. Graf
Solms-Laubach[1090] and some other authors have used _Bennettites_ for
Cycadean stems possessing strobili of known structure such as those of
_Bennettites Gibsonianus_, reserving _Cycadeoidea_ for similar stems
but without strobili sufficiently well preserved to afford evidence of
morphological characters. This practice I followed in 1895[1091], but
my usage of the two generic names has not been consistent, the name
_Cycadeoidea_ being afterwards employed[1092] in a more comprehensive
sense. The investigation of the reproductive shoots of American Lower
Cretaceous and Upper Jurassic Cycadean stems[1093] has demonstrated the
practical identity of their ovulate strobili with those of the English
_Bennettites_. It is clear that the American stems as well as numerous
specimens from Italy and other European localities are generically
inseparable from _Bennettites_. The adoption of _Cycadeoidea_ by
Wieland, following Ward, has naturally strengthened the claim of
Buckland’s genus at least so far as wide usage is concerned, and with
some reluctance I propose to fall in with this terminology and for
the sake of convenience to give up the use of _Bennettites_. Among
Mesozoic Cycadean stems agreeing with those of recent genera in habit
and in the presence of an armour of persistent leaf-bases are several
which afford no evidence either of the occurrence of fertile shoots
or of lateral shoots with terminal flowers. To such stems the name
_Cycadeoidea_ has been applied, the designation _Bennettites_ being
restricted to stems with lateral fertile shoots: this practice of
treating the absence of reproductive shoots as a characteristic feature
of _Cycadeoidea_ is regarded by Wieland as illogical and artificial;
and if, as seems probable, he is correct in believing that the majority
of the Mesozoic Cycadean plants culminated their vegetative period by
prolific development of flowers, the absence of flowering branches
would be contingent on a certain stage of development and not a generic
character. Dr Stopes[1094] has recently published facts with regard
to the anatomical features of Cycadean stems which have a bearing
on the vexed question of nomenclature, but are more important from
a morphological point of view as they indicate a closer agreement
between certain types of Lower Cretaceous stems and those of _Cycas_
and other recent genera, in which successive rings of vascular tissue
are developed, than has previously been recognised. In her diagnosis of
_Cycadeoidea_ she includes the following statement: ‘In its internal
anatomy the trunk shows two or more (up to eight are recorded) zones
of secondary wood, the zones composed of distinct series of tracheids
each more or less regularly arranged in radial sequence.’ It is
claimed that the addition of this character constitutes for the first
time a clear distinction between _Cycadeoidea_ and _Bennettites_. Dr
Stopes states that the two stems on which Buckland founded the genus
_Cycadeoidea_ are lost and adds that Buckland’s type has certain
anatomical features which are not found in _Bennettites_. Buckland
in his description of _C. microphylla_ states that there are ‘two
laminated circles’ in the stem instead of the usual single cylinder,
a character suggestive of _Cycas_. In the original figure of this
species there are no indications of any lateral fertile shoots though,
as Dr Stopes says, many of the Portland stems undoubtedly possessed
such flowers. This author makes no reference to Buckland’s later
description of _C. microphylla_: in this it is stated that the stem
bears numerous buds rising from the axillae of petioles, and these
are shown in the illustration[1095]. Without access to the actual
specimen it is impossible to say whether or not the two ‘laminated
circles’ described and figured by Buckland[1096] are two distinct
cylinders or parts of one cylinder separated by the infiltration of
some inorganic substance. In his description of _Cycadeoidea Yatesii_
Carruthers spoke of the occurrence of two cylinders of wood, and this
was confirmed in a subsequent account of the type-specimen[1097]. Dr
Stopes gives a fuller account of Carruthers’ type and re-confirm a
the existence of two vascular cylinders; she also describes a new
species, _C. buzzardensis_[1098] (fig. 578), in which there are 3–8
or more cylinders. Neither of these stems affords any evidence of the
possession of fertile shoots; they agree closely with stems of the
_Bucklandia_ type in their comparatively slender habit and differ in
this respect from Buckland’s Portland species. The occurrence of more
than one vascular cylinder in the stems _Cycadeoidea_ (= _Bucklandia_)
_Yatesii_ and _C._ (= _Bucklandia_) _buzzardensis_ suggests the
possibility that this feature was characteristic of other species
included in _Bucklandia_.
It is clear that some at least of the stems referred to the genus
_Bucklandia_ bore flowers of the _Williamsonia_ type[1099], and it is
not improbable that the stems described by Dr Stopes as _Cycadeoidea
Yatesii_ and _C. buzzardensis_ (fig. 578) possessed fertile shoots
comparable with those of the Middle Jurassic species _W. gigas_.
Dr Stopes’s contribution, while establishing a close agreement in
anatomical features between some Lower Cretaceous stems and those of
_Cycas_, does not warrant the further conclusion that these stems
were in other morphological characters closely allied to modern
Cycads. The main features of _Cycadeoidea_ may be summarised as
follows: The principal trunk is generally unbranched (fig. 507)
and identical in habit with some species of _Macrozamia_, _Dioon_,
and _Encephalartos_ (cf. figs. 379, 382); in some species, _e.g._
_Cycadeoidea Marshiana_, _C. superba_[1100], _C. nana_[1101], the
plant is represented by several approximately equal, thick, tuberous
stems, in some cases easily separated from one another: a similar
clustered habit is exhibited by certain forms of _Encephalartos_. The
size of a _Cycadeoidea_ trunk varies from a few centimetres in length
with a diameter of similar dimensions, as in _C. pumila_, to over a
metre long as in _C. gigantea_ (fig. 535), or as much as 3–4 metres in
_C. Jenneyana_ with a diameter of about half a metre. The surface is
covered with persistent leaf-bases, exactly as in many recent Cycads,
embedded in a thick mass of ramental scales which often stand out as
a prominent reticulum, the petioles having partially decayed before
the penetration of the mineralising solution through their harder
tissues (fig. 507). On the conical terminal bud preserved in some
stems (fig. 536) the foliage-leaves are replaced by linear scales.
The leaf-bases often show the vascular bundles which form a simpler
system than in the majority of recent species, their arrangement being,
as Wieland says, more Fern-like; they form a series of collateral
strands following the outline of the petiole-base[1102] with a U-shaped
invagination in the middle of the upper face (fig. 517, A). Beyond the
structure of the bundles at the base of the fronds and in the cortex
of the stem our knowledge of the anatomy of the vascular supply of
the rachises is very meagre. At the petiole-base each bundle consists
either entirely of radial rows of centrifugal scalariform tracheids and
medullary rays usually one-cell broad (fig. 519, B) or of centrifugal
and centripetal xylem in varying proportions. The ground-tissue is
well supplied with large secretory canals and in the larger leaf-bases
there is a considerable development of periderm at the surface (fig.
517, B) as in recent Cycads. The ramenta formed from the epidermal
cells consist in most species of fairly broad scales one-cell thick
at the edges and broader in the middle; in _Cycadeoidea nigra_[1103]
they are generally one-cell thick throughout and similar ramenta are
common in _C. Gibsoniana_ (fig. 517, B). In _C. micromyela_ unicellular
hairs replace the scaly ramenta, but transitional forms occur between
hairs and scales. In _Williamsonia scotica_ (fig. 562) and in an Indian
species of that genus the ramenta are exclusively long hairs as in
recent Cycads, the scale-form of the ramenta in _Cycadeoidea_ being a
Fern-character. The degree of development of the ramental tissue varies
in different species; in _C. Stilwelli_ and _C. excelsa_ it is feebly
developed while in _Cycadeoidea micromyela_ the ramenta almost cover
the exposed leaf-base armour. The exceptional abundance of the ramental
scales is a striking characteristic of some American stems referred
to a separate genus, _Cycadella_[1104]. In the abundance of the
ramental tissue, in the compact structure of the well protected cones,
and in the thickly cuticularised epidermis of the bracts and leaves
_Cycadeoidea_ exhibits xerophilous characters in a very high degree.
[Illustration: Fig. 507. _Cycadeoidea marylandica._ The first
American stem to be described. On the side of the stem shown in the
photograph there are about 30 young strobili scattered among the
leaf-bases. (After Wieland; ¼ nat. size.)]
[Illustration: Fig. 508. _Cycadeoidea Wielandi._ Transverse sections
of the secondary xylem of the stem. A, the middle region; B, the inner
edge of the xylem. (After Wieland; × 100.)]
With very few exceptions the stems of _Cycadeoidea_ so far described
afford no satisfactory evidence of the presence of more than one
vascular cylinder in the main stem: in this respect _Cycadeoidea_
agrees with such recent Cycads as _Dioon_, _Ceratozamia_, and
_Stangeria_. In the stem of C. _Jenneyana_ the secondary vascular
tissue reaches a considerable thickness and shows signs of ‘rings’
in the xylem, but these are probably the result of some periodic
interference with the uniform growth and not an indication of more
than one xylem-cylinder. The secondary xylem (figs. 508, 509) consists
only of centrifugal tracheids with some spiral elements on the inner
edge; though manoxylic, _Cycadeoidea_ has more compact wood than that
of recent Cycads; the medullary rays are 1–2 cells broad except near
the perimedullary region where they are broader and the individual
cells are tangentially stretched (fig. 508, B). The tracheids are
scalariform, but in _C. micromyela_, an exceptional type, some of the
xylem-elements have 1–2 rows of separate bordered pits (fig. 538). The
phloem (fig. 518, B) is characterised by an alternation of thick-walled
elements and thinner cells[1105]. From the main stele branches are
given off to supply the flowering shoots in the form of a cylindrical
stele like that of the primary axis, and each leaf-trace arises as
a single bundle which, in the form of a U-shaped strand (fig. 519,
A), pursues a straight course to the leaf-base (fig. 510) where it
breaks up into several branches (fig. 538, B). Both leaf-trace and
peduncle stele are given off from the lower edge of a medullary ray.
In the parenchymatous cortex large secretory canals (fig. 518, B) are
a conspicuous feature, and accessory cortical steles similar to those
in _Cycas_ occasionally occur (fig. 511). The large pith consists of
parenchyma and secretory canals, and internal periderm[1106] may be
present; no medullary bundles have been discovered.
[Illustration: Fig. 509. _Cycadeoidea Wielandi._ Tangential section
of secondary xylem of the stem. (After Wieland; × 100.)]
[Illustration: Fig. 510. _Cycadeoidea_ sp. A piece of stem showing
(A) the persistent leaf-bases in side-view and at _b_ the scars where
the bases have broken off, and (B) the inner face of the same piece
with the exposed leaf-traces passing into the leaves; one of the traces
is seen at _t_ in fig. A. (From a specimen in the British Museum; ½
nat. size.)]
[Illustration: Fig. 511. _Cycadeoidea Gibsoniana._ Stele in the
cortex. (British Museum, 8406.)]
[Illustration: Fig. 512. _Cycadeoidea ingens._ Transverse section of
a young frond, above the tip of the rachis, embedded in ramenta. The
rachis is situated on the upper side of the two ranks of pinnae. The
arrow points towards the axis of the stem. (After Wieland; × 4.)]
The correlation of the numerous fronds[1107] preserved in Mesozoic
strata with their parent-stems is seldom possible. It is known that
leaves of the _Zamites_ type were borne on stems (_Bucklandia_)
agreeing with _Cycadeoidea_ in certain features but differing in the
habit of the fertile shoots (fig. 542), and there is evidence that
similar stems bore _Ptilophyllum_ and _Dictyozamites_ fronds[1108];
but only unexpanded leaves have been found in actual connexion with
_Cycadeoidea_ stems. Wieland[1109] discovered young pinnate fronds,
agreeing in the form of the pinnae with _Zamites_ and with some forms
of _Encephalartos_, embedded in a thick mass of ramental scales in the
terminal bud of a stem: the rachises were erect and the two-ranked
pinnae imbricate and folded inwards (fig. 512), the vernation being
like that of _Dioon_ and not circinate as in _Cycas_ and Ferns. The
mesophyll of the leathery pinnae is differentiated into palisade
and lacunar parenchyma, and the bundles are said to be ‘mesarch’
though on this point more information is desirable. Each bundle is
surrounded by a sheath of thick-walled cells and the same tissue
forms =I=-shaped girders as in similar recent leaves. In one species,
_Cycadella ramentosa_[1110], the rachis of a young frond found among
the leaf-bases had a broad U-shaped vascular strand.
In most _Cycadeoidea_ stems a characteristic feature is the occurrence
of reduced leaves, or bracts, arranged spirally about a cone which
sometimes projects slightly beyond the general level of the persistent
leaf-bases, or the cones may be fully developed yet still more or less
hidden within the armour of petiole-bases (fig. 517, C). These cones,
or flowers, are borne at the apex of lateral axillary shoots, and it
is characteristic of the genus that they never project more than a
very short distance beyond the truncate stumps of the old leaf-bases.
The axis of a flowering branch bears numerous linear, hairy, bracts
(figs. 513; 514, _b_) which with their thick felt of ramenta constitute
an efficient protective investment. The summit of a fertile shoot
forms a rounded hemispherical cushion (fig. 514), or the receptacle
may be more elongate and conical (fig. 513) and in some species
pyriform[1111]. The flowers are generally bisporangiate, but the fact
that in flowers with mature microsporophylls the ovules are small and
apparently immature (fig. 513) makes it difficult to determine whether
the megasporophylls are merely immature or functionless as in the
male flower of _Welwitschia_ (cf. fig. 818). It would seem, however,
that in most cases the flowers were bisexual[1112] (fig. 513). A
remarkable feature is the enormous number of flowers on a single stem;
in _Cycadeoidea Dartoni_[1113], 54 cm. long and 35 cm. broad, 500–600
flowers were counted on one side. On the other hand the large stem of
_C. gigantea_ (fig. 536) shows no flowers. All the flowers on a single
trunk are approximately in the same stage of development: it would
seem, as Wieland points out, that after a vegetative period of some
considerable duration the plant produced a large crop of flowers, and
it is conceivable that as in _Corypha_ and some other recent Flowering
plants this supreme effort set a limit to the plant’s existence. In
the development of flowers from the old stem _Cycadeoidea_ affords a
striking example of cauliflory.
[Illustration: Fig. 513. _Cycadeoidea._ Restoration of an unexpanded
bisporangiate strobilus with some of the hairy bracts removed. Compare
_Cycadeoidea dacotensis_, figs. 529, 530. (After Wieland; _ca_ nat.
size.)]
[Illustration: Fig. 514. Ovulate strobilus of _Cycadeoidea_.
Longitudinal section showing the pith, _m_, stele, _x_, _p_, and
cortex, _c_, of the stem, the ovulate strobilus with bracts, _b_,
seeds, _s_, etc., enclosed by foliage-leaves, _l_; _a_, insertion of
leaves on the stem; _d_, insertion of disc of microsporophylls. (After
Wieland.)]
The structure of the flowers is one of the most obvious differences
between _Cycadeoidea_ and recent Cycads (_cf._ figs. 393, 394).
The bisexual flowers of the fossil stems are comparatively small,
not exceeding a few centimetres in length, like a hen’s egg or a
medium-sized pear and in marked contrast to the male and female
cones of modern Cycads (_cf._ figs. 393, 394). A verticil of pinnate
microsporophylls is attached by a circular collar formed of the
concrescent bases of the sporophylls to the lower portion of the
receptacle; each pinnule bears several shortly-stalked synangia
divided into loculi containing microspores usually with smooth walls
and similar, except in their larger size, to those of modern Cycads
(fig. 532). Sections of some microspores figured by Wieland[1114]
show what appear to be cells in the spore-cavity, but they are larger
than ordinary prothallial cells and their true nature is doubtful. We
lack information both as regards the nature of the male gametes and
the tissue formed on the germination of the spores. The free portions
of the microsporophyll-whorl may consist of as many as 20 pinnate
sporophylls, but the number is generally smaller; these are much longer
than the ovulate part of the flower and in an immature state the ends
of the sporophylls are bent inwards and downwards (fig. 513) between
the bracts and the receptacle. After expanding and shedding the spores
the whole male disc is thrown off leaving a narrow rim below the
hemispherical or conical receptacle (fig. 514, _d_). The sterile distal
end of a microsporophyll is generally slightly expanded and spathulate;
in _C. colossalis_[1115] it bears a pair of wing-like appendages (fig.
533).
The upper part of the receptacle is covered with two kinds of organs
which together form a layer of uniform depth; these are believed to be
homologous, foliar structures; the majority are sterile and have the
form of slender long and narrow appendages (fig. 514) each normally
with a single axial vascular strand. These so-called interseminal
scales increase in breadth in the apical region and form polygonal
summits less than a millimetre in breadth or exceeding 2 mm. The
low pyramidal apices of the interseminal scales give a mosaic-like
appearance to the surface of the ovulate receptacle (fig. 515). In
the lower part of the receptacle these sterile sporophylls are the
only appendages, but over the greater part of the receptacle they
are intermixed with a smaller number of similar appendages which
bear a single terminal orthotropous ovule (fig. 514, _s_). Each
ovule-bearing organ or megasporophyll (seed-stalk) is surrounded by
5—6 interseminal scales, and the narrow cylindrical micropylar tubes
are readily distinguished from the sterile sporophylls in surface-view
(figs. 516, 564). The seeds appear to be exalbuminous and the embryo
is dicotyledonous (figs. 516, 521, 523)[1116]. The seeds are very
small in comparison with those of living Cycads. The structure of
the megasporophylls, both sterile and fertile, is described in more
detail in the account of _Cycadeoidea Morierei_ and other forms. Fig.
516 represents a longitudinal section of one of the smallest seeds
of _Cycadeoidea_, between 3 and 4 mm. long; an embryo occupies the
greater part of the seed-cavity: the micropylar tube is formed of
three layers, a strong inner palisade-layer, a thin middle layer, and
an outer palisade-tissue, the interior of the tube being filled with
parenchyma; at the shoulder of the seed above the root-end of the
embryo the surface of the testa is characterised by 5–6 wings formed
by the radial extension of palisade-cells. After the shedding of the
spores and the abscission of the microsporophylls the flowering shoot
probably increased slightly in length, thus pushing the ripening seeds
beyond the ends of the surrounding leaf-bases. The ripe flowers were
eventually cut off by an absciss-layer immediately below the receptacle
(figs. 521, C, _a_; 522, _a_), large cup-like depressions being left
on the surface of the stem (fig. 534). The ovulate cone on which the
species _Cycadeoidea Morierei_ is founded probably represents the
condition of a naturally detached flower of a _Cycadeoidea_. It is
possible that the detached flowers freed from their encircling bracts
may have been edible, the small seeds being dispersed by animal agency.
[Illustration: Fig. 515. _Cycadeoidea_ sp. Surface-view of a young
ovulate strobilus showing the swollen ends of interseminal scales
grouped about the circular micropyles. (After Wieland; × 10.)]
[Illustration: Fig. 516. _Cycadeoidea Dartoni._ Longitudinal section
of seed with embryo. (After Wieland; × 19.)]
* * * * *
The splendid petrified stem, _Cycadeoidea etrusca_ Cap.[1117], one
of the treasures of the Bologna Museum, was found on a tomb 20 miles
west of that city where it was doubtless placed by the Etruscans
who obtained it from the Upper Jurassic scaly clays in the Apennine
Hills. It was in an imperfectly preserved flower of this fossil
that Graf Solms-Laubach discovered some microspores, but it was not
until Wieland’s examination of the more complete American stems that
information was obtained as to the spore-bearing organs. Another
Italian stem, _Cycadeoidea montiana_ Cap., was described in 1753 as
a ‘congeries of barnacles[1118].’ The specimen named by Goeppert
_Raumeria Reichenbachiana_[1119] was described in the middle of the
eighteenth century as a mass of _Hippurites_ or coral cups: this
was found in a swamp in Galicia and is now one of the most striking
objects in the Dresden Museum; a brief account of it is given on page
409. In 1859 Tyson discovered two large trunks in the Potomac beds of
Maryland for which Fontaine subsequently proposed the name _Tysonia
marylandica_[1120], but as Ward pointed out the species is clearly a
_Cycadeoidea_ (fig. 507). In 1894 Lester Ward[1121] recorded several
additional stems from Tyson’s locality. It is, however, from the Black
Hills of Dakota, an isolated spur of the Rocky Mountains, formed of
older rocks encircled by Lower Cretaceous strata[1122], that the
greatest number of Cycadean trunks have been obtained: the magnificent
collection now in the Yale Museum is largely due to the energy and
munificence of the late Prof. Marsh. From the Upper Jurassic beds in
Carbon Co., Wyoming[1123], several stems have been collected, and a
preliminary study of their external features led Ward to institute 20
species of a new genus _Cycadella_. Stems have also been discovered
in the Freezout Hills of Wyoming and additional specimens have been
found in the Potomac formation of Maryland. The discovery of over
1000 specimens of Cycadean stems in the Lower Cretaceous and Upper
Jurassic beds of a few localities in the United States bears striking
testimony to the abundance of these extinct Gymnosperms during the
latter part of the Mesozoic era. It is perhaps true that, as Lester
Ward wrote, ‘Cycads are to the vegetable kingdom what Dinosaurs are
to the animal, each representing the culmination in Mesozoic times of
the ruling Dynasties in the life of their age[1124].’ Although the
number of stems obtained from European countries is relatively small,
the abundance of specimens in the Upper Jurassic strata of the Isle
of Portland and Northern Italy and their occurrence in Belgium[1125],
France, Germany, Austria, Poland, India and elsewhere, together with
an abundance of Cycadean fronds in practically all Jurassic and Lower
Cretaceous plant-bearing beds, demonstrate the dominant position of
the Bennettitales. The occurrence of the genus _Williamsonia_ in
many European localities as well as in India, Afghanistan, and other
countries, and the not infrequent occurrence of stems assigned to
_Bucklandia_, _Yatesia_, _Cylindropodium_, and other genera furnish
evidence of the rich development of the Bennettitales in later Jurassic
and Lower Cretaceous floras. Wieland’s recent discovery[1126] of
numerous Cycadean fronds, _Williamsonia_ flowers, and stems in Liassic
rocks in Mexico shows that the group had already assumed an important
position in the early part of the Jurassic period.
The memoir by Carruthers[1127] on British Cycadean stems contains the
first account of the morphological features of Bennettitalean flowers
based on petrified material. In 1891 Solms-Laubach contributed an
important paper on the Bennettitean flower and several years later
Lignier[1128] contributed additional data derived from a careful
study of a well preserved strobilus[1129] from the Gault of Normandy.
Wieland’s researches[1130] added very greatly to our knowledge,
particularly with regard to the morphology of the microsporophylls.
Among the earlier descriptions of the reproductive organs of the
Bennettitales is Buckland’s account[1131] of a specimen from the
Inferior Oolite of Charmouth, Dorset (fig. 560), which he referred to
the genus _Podocarya_ (= _Williamsonia Bucklandi_[1132]): a thorough
examination of the type-specimen, which unfortunately cannot be found,
would probably furnish many important facts.
{ _Cycadeoidea_ (_Bennettites_) _Gibsoniana_ (_Carruthers_).
{ _Cycadeoidea_ (_Bennettites_) _Saxbyana_ (_Brown_).
These two species serve to illustrate the type of stem for which
Carruthers instituted the tribe Bennettiteae and the genus
_Bennettites_. _Bennettites Gibsonianus_ is the most important of the
five species described by Carruthers[1133], as it was from its fertile
shoots that information was first obtained as to the nature of the
ovulate strobili of the Bennettitales. _B. Saxbyanus_[1134], originally
described as _Cycadites Saxbyanus_ from a specimen found by Mr Saxby
at Bonchurch in the Isle of Wight and represented by Wealden examples
from Brook Point, is chiefly interesting for the clear preservation
of the anatomical features of the stem. Three other species were also
described by Carruthers; they are: _Bennettites maximus_ Carr., a large
stem similar to _B. Saxbyanus_, in the Museum of the Geological Survey;
_B. portlandicus_ from the Lower Purbeck of the Isle of Portland, in
the collection of the Geological Society; and _B. Peachianus_, a piece
of a compressed stem, in the British Museum, from the Upper Jurassic of
Helmsdale in N.E. Scotland.
[Illustration: Fig. 517. _Cycadeoidea Gibsoniana._ A, transverse
section of petiole showing vascular bundles and ramenta; B, portion of
A enlarged showing periderm and ramenta. C, tangential section of stem
with leaf-bases, ramenta (black) and two flowers, 1, 2. (A, slightly
enlarged, Manchester Collection, R, 1069; C, after Carruthers.)]
_Cycadeoidea (Bennettites) Gibsoniana._
This species was founded on a petrified portion of a large stem of
Lower Greensand age discovered by Mr Gibson in Luccomb Chine in the
Isle of Wight: the type-specimen is represented by pieces of the
original block in the British Museum and in one of the Museums at the
Royal Gardens, Kew. The following description is based partly on the
published accounts and in part on an examination of sections in the
British Museum, the Manchester University Museum, and in Dr Scott’s
collection.
The elliptical form of the stem and vascular cylinder as seen in
transverse section, regarded by Carruthers[1135] as a feature
characteristic of the genus, has no morphological significance and is
in part at least due to compression. In the large pith, the armour of
persistent petiole-bases separated by dense ramental scales (fig. 517,
A, B), and in habit, _Cycadeoidea Gibsoniana_ agrees generally with
the stems of many recent Cycads, but the resemblance of the vegetative
organs is in marked contrast to the differences exhibited by the
reproductive shoots. The pith consists of parenchyma with scattered
secretory ducts but no medullary vascular bundles. In the pith of
_Cycadeoidea Peachiana_ there are patches of tissue superficially
resembling vascular strands, but these are probably bands of internal
phloem like those described by Solms-Laubach[1136] in some Italian
stems. In none of the English stems are there any clear indications of
the occurrence of more than one cambium in the stele. The secondary
xylem is entirely centrifugal with some smaller crushed elements,
presumably protoxylem, at the inner edge where the medullary rays are
especially broad. The xylem is of the manoxylic type (fig. 518, A)
as in recent Cycads; though the medullary rays, 1–2 cells broad, are
rather smaller than in recent species. The tracheids are scalariform
as in _Stangeria_ (fig. 397). As in recent Cycads there is a broad
cylinder of secondary phloem (fig. 518, B)[1137] composed of alternate
layers of thick-walled and thinner elements—sieve-tubes and parenchyma:
traces of lateral sieve-plates occur on some of the elongated elements.
Each leaf-trace arises as a single strand from the lower edge of a mesh
formed by the large inner end of a medullary ray: on emerging into
the inner cortex the trace has the form of a U-shaped strand (fig.
519, A, _lt_) which passes direct to the petiole, following a steeply
ascending course in _Cycadeoidea Saxbyana_ and almost horizontal in _C.
Gibsoniana_. Before entering the base of a leaf the trace breaks up
into several collateral strands and these form a simple pattern as
seen in a tangential section of the leaf-bases (fig. 517, A, C), the
central bundles on the upper side forming a U-shaped involution. There
is no indication of any girdling of the foliar bundles. The arrangement
of the petiolar bundles is simpler and more Fern-like than in the
majority of existing Cycads. Each vascular bundle consists in the
petiole-base mainly of centrifugal secondary xylem and medullary-ray
tissue (fig. 519, B); a group of centripetal tracheids is usually
recognisable internal to the protoxylem: the structure is of the
mesarch type with a variable amount of centripetal xylem, and agrees
generally with that in recent Cycads.
[Illustration: Fig. 518. _Cycadeoidea Gibsoniana._ A, secondary xylem
of stem; B, secondary phloem and part of the cortex with secretory
ducts, _s_. (A, B, British Museum, 13206.)]
[Illustration: Fig. 519. _Cycadeoidea Gibsoniana._ A, transverse
section of the vascular cylinder of stem, with leaf-trace, _lt_; _c_,
cambium, _px_, protoxylem. B, vascular bundle of petiole. (British
Museum.)]
The comparatively narrow cortex is composed of parenchyma with
scattered secretory sacs (fig. 518, B, _s_), and occasionally an
elliptical vascular strand (fig. 511) is present which is probably
cauline as are the similar strands in _Cycas_. The persistent
petiole-bases are covered with ramental scales which form a dense
interfoliar packing: these frequently consist of a single layer of
fairly thick-walled cells or, as seen in transverse section, of
spindle-like scales one-cell thick at the edges and 2–3 cells broad in
the middle (fig. 517, B).
[Illustration: Fig. 520. _Cycadeoidea Gibsoniana._ Ground-tissue of
bract. (British Museum. 41388.)]
The presence of fertile shoots, presumably axillary, is one of the most
striking features of Bennettitean stems. The branching is monopodial
and not sympodial as in most recent Cycads. The nearest approach to
the method of branching in _Cycadeoidea_ is afforded by some stems
of _Macrozamia_ recently described by Chamberlain[1138]. It is not
improbable that some of the flowering branches of _Cycadeoidea_
were branched. Solms-Laubach[1139] states that he observed certain
characters in the secondary axes of _Cycadeoidea Gibsoniana_ which led
him to suspect that there may have been fascicled systems of fertile
shoots emerging in a body or in close proximity to one another between
the leaf-bases of the stem. An example of a branched flowering shoot
is described in _Williamsonia scotica_[1140]. A fertile shoot agrees
in structure with the main axis and Scott[1141] states that the phloem
is particularly well developed, a feature by no means unusual in
fertile branches. These lateral shoots (fig. 514) bear numerous linear
bracts each with three collateral vascular bundles, and ground-tissue
composed of thick-walled cells characterised by scalariform pitting
(fig. 520): secretory sacs are abundant. The hypodermal stereome is
especially developed on the inner face of the bracts. The apex of a
lateral shoot has the form of a rounded cushion (figs. 514; 521, A, C)
similar to the receptacle of many Composites, and on this are borne the
sporophylls. It is characteristic of _Cycadeoidea_ that the flowers
project very slightly beyond the surface of the stem and the peduncles
are not exposed except in tangential sections through the leaf-base
armour (fig. 517, C, 1, 2). On the fall of the flower or ripe ‘fruit,’
which is effected by an absciss-layer (figs. 521, C, _a_; 522, _a_),
a cup-like scar is left on the stem (_cf._ fig. 534). This method of
flower-production suggests comparison, _mutatis mutandis_, with the
phenomenon of cauliflory in certain recent Flowering plants; it is one
of the distinguishing features between _Cycadeoidea_ and stems bearing
longer fertile shoots with flowers of the _Williamsonia_ type.
[Illustration: Fig. 521. _Cycadeoidea (Bennettites) Gibsoniana._
A, C, longitudinal sections; _a_, absciss-layer; _b_, bracts; _pr_,
‘pericarp’; _s_, scales, sterile and fertile. B, transverse section
of female flower; _i_, interseminal scales; _m_, megasporophylls. D,
transverse section of seed showing the testa, _t_, separated by a
space, _sp_, from the embryo. E, embryo; _r_, radicle. (A, B, D, E,
after Solms-Laubach; C, section in the British Museum.)]
Fig. 517, C, shows a tangentially cut surface of a portion of the stem
of _Cycadeoidea Gibsoniana_ with two axillary fertile shoots; one,
1, is cut across below the receptacle and shows the axis surrounded
by bracts while the other, 2, is seen at a higher level, above the
receptacle, where the section has exposed the numerous sporophylls.
The rounded surface of the receptacle is covered with a dense cluster
of long slender appendages, seed-stalks and interseminal scales, the
latter being much more numerous than the former (fig. 521, A, B). These
organs are believed to be homologous foliar structures, the seed-stalks
being megasporophylls and the interseminal scales abortive or potential
sporophylls (see also figs. 562, 563). Fig. 514 shows the form of a
single flower from an American stem closely allied to _Cycadeoidea
Gibsoniana_.
[Illustration: Fig. 522. _Cycadeoidea Gibsoniana._ Longitudinal
section of flower showing half the receptacle with part of the
absciss-layer, _a_. (British Museum.)]
[Illustration: Fig. 523. _Cycadeoidea Gibsoniana._ Seed with embryo.
(British Museum, 41388.)]
The megasporophylls are more or less polygonal in transverse section:
there is a central concentric vascular strand surrounded by a thick
cortex (fig. 527): at its upper end the sporophyll bears a single
orthotropous seed containing a dicotyledonous embryo (figs. 521, D, E;
523). The vascular strand pierces the base of the testa and expands
to form a shallow cup of tracheal tissue in the chalaza; there are no
bundles in the single integument. The testa (fig. 521, D, _t_) consists
of three regions, a median layer of rather large rectangular or
palisade-cells with an inner and outer tissue composed of much smaller
cells. The testa is prolonged distally as a slender cylindrical column
or micropylar tube at the base of which it becomes broader owing to
the increase in breadth of the middle or palisade layer. A nucellar
beak projects as a cone into the base of the micropylar tube. No
pollen-chamber has been found. It is noteworthy that the micropyle is
closed in the ripe seeds. Internal to the testa there is a crushed
membrane separated from the embryo by a space (fig. 521, D, _sp_): this
is the remains of the nucellus and, as Solms-Laubach points out, there
is no proof that any endosperm was present in the ripe seeds[1142].
The embryo consists of a short axis, the conical radicle and the very
short apex of the epicotyl, also two equal cotyledons each with a
few vascular bundles (fig. 521, D). The long interseminal scales, as
seen in transverse section in the lower part of a flower between the
sporophylls, appear as compressed polygonal organs (fig. 521, B, _i_)
with an axial vascular strand surrounded by parenchyma and limited by
a strong epidermis; they pass up between the seed-stalks, _m_, and in
the distal end become considerably enlarged (figs. 514, 515), gradually
expanding to form a truncate or slightly pyramidal apex (figs. 553,
563). The swollen peltate apices of adjacent scales form a continuous
covering to the flower interrupted, except in the lower sterile part
of the flower, by symmetrically disposed cylindrical micropylar tubes
(fig. 515). The peripheral interseminal scales form a homogeneous
parenchymatous tissue which springs from below the edge of the
receptacle (fig. 521, A, B, _pr_) and the individuality of the scales
composing this ‘pericarp’ is indicated by occasional invaginations of
the epidermal layer which marks the boundary of the polygonal areas.
The structure of the megasporophylls and scales is more fully described
in the case of _Cycadeoidea (Bennettites) Morierei_[1143].
The flowers of _Cycadeoidea Gibsoniana_ appear to be unisexual and
ovulate: in view of the discovery by Wieland of numerous bisexual
fertile shoots on American species of _Cycadeoidea_ it would be
reasonable to regard the apparently unisexual flowers of the English
species as originally bisexual but preserved at a stage subsequent to
the loss, by abscission, of the disc of microsporophylls. Fig. 514
shows a flower of an American _Cycadeoidea_ practically identical with
those of _C. Gibsoniana_, but the remains of the staminate disc are
clearly seen at _d_ below the swollen apex of the flowering axis. In
the photograph of half of the same region in _C. Gibsoniana_ reproduced
in fig. 522 there is no indication of any similar trace of a whorl of
microsporophylls. Admitting the fact that a shrivelled remnant of the
persistent base of a whorl of microsporophylls might easily escape
observation, it is difficult to believe that any fertile leaves ever
existed in the flower represented in figs. 521, 522. It is equally
difficult to regard the specimen represented in fig. 561 as other than
a true unisexual (ovulate) flower.
_Cycadeoidea (Bennettites) Morierei_ (Saporta and Marion).
The name _Bennettites_ was adopted by Lignier for this species which
was founded on a detached flower from the Gault[1144] of Vaches-Noires,
Normandy. It was first described by Morière[1145], then by Saporta and
Marion[1146], who named it _Williamsonia Morierei_, and it has since
been thoroughly investigated by Lignier[1147]. There is no evidence as
to the nature of the parent-stem though Morière suggested a possible
connexion with _Zamia Brongniarti_ Mor. (figured by Saporta[1148]
as _Fittonia Brongniarti_) from the same locality. There can be no
reasonable doubt that _Bennettites Morierei_ was borne on a lateral
branch of a stem of the _Cycadeoidea_ type: it is constructed on
essentially the same plan as the flowers of _Cycadeoidea (Bennettites)
Gibsoniana_, and in both cases there is no indication of the presence
of microsporophylls. The type-specimen is 5·5 cm. long and 3·5
cm. broad, ovoid, and characterised by a depressed cushion-like
receptacle as in _Cycadeoidea Gibsoniana_. The enveloping bracts
with their ramental scales agree generally in structure with those
of the English species and, except as regards the ramenta, with
_Williamsonia scotica_: numerous stomata occur on the lower surface;
the ground-tissue consists of thick-walled parenchyma and the narrow
pit-canals simulate the scalariform bands in _Cycadeoidea Gibsoniana_
(_cf._ fig. 520). The pitted sclerous cells in the bracts of _W.
scotica_ are of the same type. There is an anastomosing system of
secretory canals, also several vascular bundles like those in _C.
Gibsoniana_ but more numerous; the latter are composed of a group of
phloem-elements abutting externally on fibres, a well-defined cambium,
and radially disposed scalariform tracheids: internal to the protoxylem
is a group of elements considered by Lignier to be centripetal xylem.
From the branching and slightly divergent course of the bundles in the
upper part of the bracts Lignier concluded that these organs represent
the basal portions of leaves originally provided with a terminal limb.
It may be that the small lateral appendages to some of the bracts of
_Williamsonia scotica_ (fig. 561, _l_) afford support to this view.
_Megasporophylls_ (seed-stalks and seeds). These organs, 3–4·5 cm. long
and approximately 1·5 mm. in diameter, are in most cases imperfectly
preserved. In transverse section and at a level of 1 cm. above the
receptacle a stalk bearing an atrophied seed shows the following
features: an epidermis with very thick internal walls encloses a
parenchymatous ground-tissue with an axial conducting strand. At a
higher level the epidermal cells have walls of uniform thickness, and
a hypodermal layer of cells with coloured contents is differentiated
from the ground-tissue (fig. 524, D, _ac_). As the seed-base is
approached the epidermal cells tend to separate from one another and
divide longitudinally, the compact epidermal layer being replaced
by an envelope of tubular, dissociated, cells (fig. 524, D, _Et_).
Similar tubular elements occur in the seed-stalks of _Cycadeoidea
Gibsoniana_. A fully developed seed-stalk bearing a complete seed cut
across in the middle region shows the following features: a concentric
vascular strand surrounded by thin-walled parenchyma and the coloured
hypodermal layer (fig. 524, D, _ac_), the whole being enclosed in the
tubular envelope of epidermal origin (_Et_) which is more strongly
developed than in the stalks of imperfect seeds: there may be as many
as 10–12 tubular cells on one radius. When traced downwards towards
the receptacle the tubular envelope decreases in breadth, though
the cells become more numerous and smaller, until in the immediate
neighbourhood of the receptacle the tubular tissue is transformed into
a compact parenchyma of large cells each of which corresponds to a
group of tubes formed by the septation of the cells. Traced upwards
this thin-walled parenchyma gradually passes into thick-walled tubes,
and near the seed-base the tubular envelope is reduced to two layers,
an inner consisting of relatively small cells with sinuous radial walls
(the folded layer of Lignier) and an outer tubular layer. Lignier
describes an interesting abnormality, a bifid seed-stalk enclosed in a
common epidermis which he compares with the occasional branching of the
seed-stalks of _Ginkgo biloba_.
[Illustration: Fig. 524. _Cycadeoidea (Bennettites) Morierei._
A. Transverse section of the micropylar tube containing the apex of
the nucellus; _Ei_, inner epidermis; _Tf_, ground-tissue; _e_,
outer epidermis with the thickening of the walls shown in a few of
the cells.
B. Transverse section of the upper part of the micropylar tube;
lettering as in fig. A.
C. Transverse section at the level of the wings formed by the fibrous
layer and corresponding to the angles of the seed, approximately at
the level _cp_ in fig. 525; _cn_, nucellar cavity; _Ei_, inner
epidermis of seed-coat; _cf_, fibrous layer of wings, _f_, which
extend across the fleshy layer, _tch_, to the radial layer _ar_
(_cf._ fig. 525); _at_, tubular layer; _Ee_, epidermis of adjacent
scale detached from the other tissues, _ase_, along the line of
fracture _d_; _EE_, epidermis of two adjacent scales.
D. Transverse section of peduncle; _tr_, tracheids; _ac_, coloured
subepidermal layer; _Et_, tubular epidermis, double in places;
_EE_, epidermis formed from neighbouring scales. (From Prof.
Lignier’s drawings; A, B, D, × 118; C, × 90.)]
_Seeds._ The seeds (figs. 525, 526), 6–7 × 2·5–3 mm., are tetragonal or
pentagonal in the upper half (fig. 527, 1, 2), the angles being formed
by thick but not very prominent wings of tissue (fig. 524, C, _cf_);
they are orthotropous and have a single integument (figs. 525, 526).
The tubular layer forming the outer portion of a seed-stalk near the
seed-base is prolonged over the surface of the testa as a discontinuous
covering in the form of isolated or small groups of tubes, giving a
striated appearance to the seeds. This layer though apparently a part
of the seed is derived from the neighbouring interseminal scales of
which it is the epidermal layer; it consists of elongated cells and
scattered stomata[1149]. The folded layer persists only in the lower
part of the seed, being replaced by a layer of radially extended cells
(radial layer; _ar_, figs. 524, C; 525, _ar_; 527, _c_) in the upper
region of the seed. In the micropylar region both the tubular and
folded layers undergo further change; the external, tubular, layer
forms a kind of epidermis (_at_, figs. 524, 525), the subepidermal
layer, consisting of the radially elongated cells (figs. 524, 525,
_ar_; 527, _c_). The superficial layer assumes a different aspect in
the micropylar region, its cells being thicker walled, as are also
those of the subepidermal layer (fig. 524, A and B). The micropylar
canal (figs. 524, 525, _cm_) is cylindrical in the lower part but at
the apex is reduced to a long and narrow slit bounded by an internal
epidermis of radially stretched cells which in the lower portion of
the tube are thinner walled and isodiametric. The rest of the testa is
differentiated into two regions; an outer fleshy region immediately
internal to the folded (or radial) layer and an inner fibrous region
next the nucellus, which is one-layer broad between the wings but
opposite the wings it extends radially outwards across the fleshy
tissue to the radial layer (figs. 524, C; 525; 527): in the winged
portion of the seed this tissue forms the inner fibrous portion of the
wings but in the lower part of the seed below the wings it forms a
single layer of uniform breadth finally spreading out as a basal cup
in the chalazal region where it is pierced by the vascular strand. The
fleshy portion of the testa forms one layer in the proximal part of
the seed and becomes several layers wide between the fibrous wings
in the upper part. This fleshy tissue appears to be derived from the
coloured, subepidermal, layer of the seed-stalk, while the internal
parenchyma is regarded by Lignier as the equivalent of the fibrous
layer of the testa. In the micropylar tube the fibrous layers are
replaced by 2–3 layers of sclerous cells (fig. 524, A, B). The testa
has no vascular supply: the concentric strand of the seed-stalk passes
through the fibrous tissue at the base of the seed and reaches the
base of the nucellus (fig. 525). The nucellar apex extends into the
lower part of the micropyle (fig. 525, _n_), and in some cases Lignier
noticed an axial canal formed by the breaking-down of the cells which
abutted below on a cavity above the embryo, probably the remains of
a pollen-chamber (figs. 525, 527). No microspores have been found.
Two dark spots shown at _co_, fig. 525, may represent archegonia but
this is doubtful, especially as the seed contains a well-developed
embryo. The nucellus is free from the testa only in the apical region
and a dicotyledonous embryo occupies the interior without any trace of
endosperm. Lignier points out that in some seeds containing embryos the
nucellar beak is not completely perforated: in this fact and in the
absence of microspores in the micropylar canals he is inclined to see
evidence of parthenogenesis[1150].
[Illustration: Fig. 525. _Cycadeoidea (Bennettites) Morierei._
Section of a seed and adjacent interseminal scales. _tm_, micropylar
tube; _n_, nucellar beak in the micropylar canal, _cm_; _cp_,
pollen-chamber; _co_, archegonia (?); _em_, position of the embryo;
_ch_, chalaza; _dn_, remains of the nucellus; _af_, fibrous layer
passing below into the shell, _cq_, and the peduncle, _Tf_; _tch_,
fleshy layer; _ar_, radial and tubular layers represented in the
peduncle by the tubular envelope _at_; _Ec_, swollen ends of the
interseminal scales. (From a drawing kindly supplied by Prof. Lignier;
× 10.)]
[Illustration: Fig. 526. _Cycadeoidea (Bennettites) Morierei._
Longitudinal section of a seed and interseminal scales. (From a
photograph supplied by Prof. Lignier.)]
In several respects the seeds of _Cycadeoidea_ agree with those of
_Gnetum_: reference should be made to the account of the seed of
_Gnetum africanum_ in Chapter +lii.+ and to the papers referred to in
the footnote[1151].
_Interseminal scales._ The young seed-stalks agree very closely
with the interseminal scales: each seed-stalk is surrounded by 5–6
scales (fig. 527) as in other Bennettitean flowers (fig. 564).
For the greater part of their length the interseminal scales are
compressed, but above the seeds, where they are free from pressure
(fig. 526), they become much thicker and form a covering (‘pericarp’)
as in _Cycadeoidea Gibsoniana_. In its upper region an interseminal
scale consists of an epidermis with strongly thickened inner walls,
hypodermal thick-walled cells and parenchymatous ground-tissue with
a single axial bundle. In the lower part the scale is more flattened
and the thick-walled hypoderm is replaced by thin-walled parenchyma.
Some of the scales at the periphery of the receptacle where there are
no seed-stalks are broader and may have six vascular bundles; this,
Lignier suggested, might be regarded as evidence of the reduction of
the interseminal scales from leaves possessing a terminal limb; but a
further examination of scales at the periphery of the flower led him
to the conclusion that the distal swelling of the scales is solely due
to the hypertrophy of conjunctive tissue and is not the result of the
modification of a reduced limb[1152]. The morphological value of the
interseminal scales and seed-stalks has not been definitely settled,
though the probability is that they are homologous organs and foliar.
Solms-Laubach[1153] suggested that both may be axial, the seed-stalks
representing axes ending in a flower reduced to a single ovule; or,
he adds, the seed-stalks may just as well be carpels, though in that
case we should have the unusual phenomenon of terminal seeds. The
interseminal scales may be aborted seed-stalks crushed between the
latter; or if the seed-stalks are axes, the scales may be foliar. He is
inclined to see in the scales the bracts and prophylls of seed-stalks
to which must be added such bracteoles, preceding the seed or flower,
as may happen to spring from the seed-stalks. Pearson[1154], on the
assumption that the seed-stalks are axial structures, institutes a
comparison between _Welwitschia_ and _Bennettites_ and regards each
flower of _Welwitschia_ as a much reduced Bennettitean strobilus.
Lignier believes the interseminal scales to be leaves borne on the
swollen apex (receptacle) of an axis of the second order, while the
seed-stalks are fertile leaves of a unifoliar bud of the third order
possibly axillary though not necessarily so to the interseminal scales.
My own view, influenced by the examination of the immature flower of
_Williamsonia scotica_, is that the seed-stalks (megasporophylls) and
scales are homologous, the former being sporophylls and the latter
sterile foliage leaves, the whole flower, as Wettstein[1155] says,
consisting of a conical axis bearing numerous fertile and sterile
carpels enclosed by a perianth of bracts. Worsdell[1156], who shares
Čelakovsky’s opinion that sporophylls were originally radially
symmetrical organs bearing a terminal sporangium, regards the flowers
of _Cycadeoidea Gibsoniana_ and other species as more primitive
than those of recent Cycads: he does not see any justification for
the view that the Bennettitalean flowers are in advance of those of
existing Cycadean plants as regards a supposed tendency towards the
Angiospermous type. He maintains that _Bennettites_ ‘shows absolutely
no indication of such an advanced structure in its essential organs,
the sporophylls, which remain primitively radial in structure, bearing
the ovules in a terminal position.’
[Illustration: Fig. 527. _Cycadeoidea Morierei._ Transverse section
of interseminal scales and seeds near the apex of the latter; seeds 1
and 2 show the pollen-chamber, _a_; the fibrous layer, _b_, forming
wings and extending across the fleshy tissue; _c_, the radial layer;
seeds 3 and 4 are aborted. (After Lignier.)
The letters _a_, _b_, _c_, in this figure correspond to _cp_, _cf_, and
_ar_ in figs. 525, 526.]
_Cycadeoidea dacotensis_ (McBride).
McBride[1157] first described this Lower Cretaceous species from the
Black Hills of South Dakota as _Bennettites dacotensis_, the generic
name _Cycadeoidea_ being adopted by Ward[1158] who distinguished
some of McBride’s specimens as _Cycadeoidea McBridei_. The stem is
elliptical in section, 32 cm. long and 45 cm. in girth: owing to the
partial decay of the petiole-bases the ramental reticulum forms a
prominent feature. Numerous flowers, all of which are approximately
at the same stage of development, project like conical buttons above
the general level of the stem-surface[1159]. The bisporangiate flowers
consist of a conical receptacle bearing interseminal scales and
megasporophylls, the whole being surrounded by spirally disposed
bracts (fig. 529). A whorl of 18 or 19 nearly mature microsporophylls
is attached to the base of the receptacle (figs. 528, 530); each
microsporophyll has a strong rachis extending beyond the apex of the
flower-axis and bent inwards and downwards with the distal end tucked
between the ascending rachis and the receptacle. The slender pinnules,
in two alternate series, are bent downwards and bear synangia in rows.
A transverse section just below the ovulate portion of the cone shows
a continuous ring of tissue encircling the receptacle with vascular
bundles parallel to the surface (fig. 530, _A_, _m_); at a higher level
the bundles fall into groups preparatory to the breaking up of the
disc into separate microsporophylls. Immediately above the apex of the
central cone the coherent basal portion of the verticil of sporophylls
is replaced by the separate rachises which in section have the form
of isosceles triangles (fig. 530, _B_). Each microsporophyll is
approximately 10 cm. long; the longest pinnule being 1·5 cm. in length
and bearing two lateral series of synangia, 10 in each row. At maturity
the microsporophylls probably spread out and the whole whorl was thrown
off leaving an annular rim (fig. 514, _d_) such as is often seen at the
base of older ovulate strobili. The immaturity of the ovules in this
(fig. 528) and other specimens led to the suggestion that the strobili
of _Cycadeoidea_ were protandrous. The synangia (fig. 531) are several
times broader than long and similar in size to those of the Fern
_Marattia_. In each synangium are two rows of elongated loculi (fig.
532) containing oval microspores usually with a smooth exine and rather
larger than those of recent Cycads. The synangium-wall is composed of a
palisade-layer of thick-walled cells and a layer of smaller and thinner
cells: the palisade-layer is narrowest at the apex where dehiscence
occurs and broadest at the base where the hypodermal tissue is more
abundant and forms a short thick pedicel. The two rows of loculi are
bounded by flattened cells and there are 10–20 loculi in each of the
two rows: dehiscence of the individual loculi occurs in the middle of
the inner wall.
[Illustration: Fig. 528. _Cycadeoidea dacotensis._ Longitudinal
section through a bisporangiate strobilus; _s_, folded microsporophylls
with synangia; _o_, receptacle bearing short megasporophylls and
interseminal scales; _a_, eroded surface of bracts; _r_, ramenta
between the bracts and leaf-bases; _l_, leaf-base; _c_, cortex of stem;
_t_, vascular cylinder of peduncle. (After Wieland; nat. size.)]
[Illustration: Fig. 529. _Cycadeoidea dacotensis._ Transverse
sections of a young ovulate strobilus. A, near the summit of the
strobilus 2 cm. below the surface of the armour of leaf-bases, showing
numerous bracts surrounding the receptacle and embedded in a mass of
ramenta, also sections of some leaf-bases with vascular bundles. B,
in this section, 2·5 cm. below A, the peduncle of the strobilus is
seen with a cylinder of vascular bundles; _b_, a bract belonging to an
adjacent strobilus. (After Wieland; nat. size.)]
[Illustration: Fig. 530. _Cycadeoidea dacotensis._ Transverse
sections through a bisporangiate strobilus. A, showing the receptacle
with its interseminal scales and ovules, the continuous disc of
microsporophylls, _m_, with vascular bundles, and the separate (_m′_)
infolded portions of the microsporophylls with some synangia; bracts
and ramenta. B, this section, cut above the apex of the receptacle,
shows the microsporophylls and synangia. (After Wieland.)]
[Illustration: Fig. 531. _Cycadeoidea dacotensis._ Synangia exposed
by weathering and showing the radially disposed loculi. (After Wieland;
× 6.)]
_Cycadeoidea Marshiana_ Ward.
[Illustration: Fig. 532. _Cycadeoidea dacotensis._ Synangium in
longitudinal section showing the thick pedicel, the line of dehiscence,
and two loculi with a few microspores. (After Wieland; × 40.)]
This Lower Cretaceous Black Hills species[1160] affords an admirable
example of a method of branching exhibited by some stems: as shown in
Wieland’s photographs[1161] there may be five or six large and massive
trunks all in the same stage of fructification, differing but little
in size and forming a cluster resembling independent plants growing in
close proximity to one another. There is apparently no central or major
axis and the habit is therefore very different from that of a branching
_Bucklandia_. _Cycadeoidea Marshiana_ bore large ovulate pyriform
strobili projecting slightly beyond the leaf-bases; they are 5 cm. long
with a maximum diameter of 3·5 cm. and have an elongated receptacle
bearing short scales and sporophylls. The apical bud of one of the
trunks shows particularly well in transverse section the dense ramental
packing between the bud-scales[1162]. Similar clusters of short and
thick trunks occur in _Cycadeoidea superba_ and other American species.
In the small bisporangiate flowers of this species[1163] the
microsporophylls, 11 or 12 in the verticil, are characterised by
the presence of a ventral furrow which, as Wieland suggests, may be
comparable on a much simpler scale with the winged sporophylls of
_Cycadeoidea colossalis_ (fig. 533). The disc splits up at a distance
of 1 cm. above the apex of the receptacle into the microsporophylls,
each of which is 5·5 cm. long and bears two rows of pinnules which
in the middle region have a length of 1 cm.; a microsporophyll is
elongate, elliptical, and acuminate. In this species as in some others
there is a brush of sterile scales at the apex of the receptacle.
_Cycadeoidea colossalis_ Ward.
Wieland[1164] has recently described some interesting features in the
microsporophylls of a bisporangiate flower assigned to this Lower
Cretaceous species from the Black Hills illustrating a departure from
the usual type. The hairy bracts extend considerably above the apex
of the flower-proper; in fig. 533, A, a transverse section above
the receptacle, they are shown grouped about a circle of V-shaped
structures, converging towards a central point, which are the sterile
prolongations of the ten rachises of the free portions of the staminate
disc. Each rachis is divided by a deep ventral furrow into a pair
of wings (fig. 533, B, C), and it is these pairs of wings that form
the V-shaped structures in fig. 533, A. The wings form a dome-like
group above the flower-apex (fig. 533, D, E). The synangia are borne
in two rows on the concrescent disc and on the free sporophylls,
which in this type are much simpler than in other species and agree
in the absence of pinnules with some forms of _Williamsonia_ (_cf._
fig. 556). The receptacle is pyriform and bears very short scales and
seed-stalks; from its apex several interseminal scales are prolonged
as a terminal brush, a feature of interest in connexion with flowers
of _Williamsonia_. Wieland compares the wings of the microsporophylls
to the two horns on the distal surface of the corresponding organs of
_Ceratozamia_ and draws a comparison between them and the canopy of
some Palaeozoic seeds, but it is doubtful whether homologies can be
established between these elaborate sporophylls and the integuments of
Pteridosperm seeds[1165].
_Cycadeoidea Reichenbachiana_ (Goeppert).
Goeppert referred this species to his genus _Raumeria_[1166], a generic
name retained by Carruthers though, as Solms-Laubach[1167] points
out, the abundance of lateral fertile shoots among the leaf-bases
shows it to be essentially similar to _Cycadeoidea Gibsoniana_.
The type-specimen in the Dresden Museum is a splendid example of
a fossil cycadean stem; it is probably of Lower Cretaceous age,
but was found in Galicia as an isolated specimen. It consists of a
portion of a cylindrical trunk similar in habit to _C. gigantea_,
·5 met. high and about the same in diameter. The pith, according to
Schuster[1168], is 13 cm. in diameter and the xylem 8 cm. broad. There
are many flowering shoots some of which are represented by cup-like
depressions, the base of the cup consisting of the cylindrical axis
and the sides bearing the impress of the encircling bracts (fig.
534). Goeppert compared these lateral shoots with the buds frequently
produced on the stems of _Cycas_. It is interesting to find that some
of the cups correspond very closely in size with _Williamsonia_
flowers, another indication of the very close agreement between the
_Williamsonia_ and _Bennettites_ types of strobili. Some flowers
still in place show 16 bipinnate microsporophylls that were petrified
before the synangium-bearing fronds unfolded[1169]. The ramental
scales and other tissues figured by Schuster are of the usual type. A
second specimen found as a boulder in Silesia and named by Goeppert
_Raumeria Schulziana_ may, as he suggests, be a younger example of _C.
Reichenbachiana_. Another Galician stem, probably also Lower Cretaceous
in age, is described by Raciborski[1170] as _Cycadeoidea Niedźwiedzkii_.
[Illustration: Fig. 533. _Cycadeoidea colossalis._ Diagrammatic
restorations of the bisporangiate flower. A, transverse section above
the receptacle showing the bracts (black), a petiole with vascular
bundles, ramenta, and (1–10) the wings of the microsporophylls. B, C,
longitudinal section of flower showing the receptacle with the small
megasporophylls, the staminate disc with winged microsporophylls
and synangia, and the terminal brush of interseminal scales
(indicated by the arrow in B). The megasporophylls and synangia are
represented larger than the actual size. D, this shows on one side
the dome-like arrangement of the microsporophylls and, on the right,
a microsporophyll in side-view. E, longitudinal section as far as the
plane _T_ surmounted by the apex of the collection of microsporophylls,
_c_; _s_, microsporophyll with synangia; _A_, recurved apex of
microsporophyll; _B_, bracts; _D_, insertion of disc; _L_, outer bracts
next the petiole bases. (After Wieland; _ca._ nat. size.)]
[Illustration: Fig. 534. _Cycadeoidea Reichenbachiana._ Cup-like
cavity on the stem showing the axis and surrounding bracts of a lateral
fertile shoot. (After Schuster, from a block kindly supplied by Prof.
Rothpletz.)]
_Cycadeoidea gigantea_ Seward.
This species is founded on a large stem from the Upper Purbeck series
of the Isle of Portland[1171] where it was discovered in a shaly clay
17 ft above the great Dirt bed which yielded the trunks described
by Buckland and other authors (fig. 535). The stem (fig. 554) is 1
met. 18 cm. high and has a maximum diameter of 1 met. 7 cm. It is the
tallest fossil Cycadean stem so far found in a single piece though
_Cycadeoidea Jenneyana_ probably reached a greater height. The stem
is elliptical in section (fig. 537), a form due in part at least
to compression. The only tissues preserved are in the superficial
region of the persistent leaf-bases. As the result of decay before
mineralisation many of the petiole-bases are represented by cavities or
meshes in a prominent reticulum of silicified ramental scales. Towards
the apex the leaf-bases are smaller and a conical bud surrounded by
linear scale-leaves occupies the summit: an irregular cap of ramental
scales forms the apex of the terminal bud. In section the bud would no
doubt present an appearance like that shown in Wieland’s photograph
of the terminal cone of _C. Marshiana_[1172]. There is a striking
resemblance both in the ramental cap and in the form of the protective
scales between the fossil stem and such a Cycad as _Encephalartos
Altensteinii_[1173]. A remarkable feature of _C. gigantea_ is the
absence of any fertile shoots among the leaf-bases. In one tangential
section a small bud was found, but it affords no evidence of the
presence of any reproductive organs. A similar bud is described by
Lignier[1174] in the stem of _C. micromyela_. The absence of lateral
flowers is, however, hardly a sufficient reason for separating this
stem generically from other species of _Cycadeoidea_: negative evidence
in this case is of doubtful value. While it is possible that the
strobili were terminal as in most recent Cycads, it is more probable
that they were lateral. The surface-features, though not perfect,
are for the most part sufficiently well preserved to enable one to
recognise the bract-encircled axes of strobili were any present. If as
Wieland believes, and he is probably correct, the production of flowers
was the culminating event in the life of these Cycadean plants, the
absence of fertile shoots is merely an expression of immaturity. It is,
however, difficult to understand how lateral branches could find their
way to the surface among the crowded and cork-covered leaf-bases of the
stem. The absence of flowers may be due to some unfavourable external
conditions. The petioles consist of parenchymatous ground-tissue with
many secretory sacs and in some cases twelve partially preserved
vascular bundles: the xylem consists of radial rows of centrifugal
tracheids and medullary rays, but it is not possible to say whether
any centripetal xylem was present. A fairly thick band of phelloderm
and periderm, apparently subepidermal in origin, forms the peripheral
tissue, and in places epidermal cells with attached ramenta are
clearly preserved. The ramenta are of the type characteristic of the
majority of fossil Cycadean stems. Stomata were found showing a pair of
guard-cells and apparently two subsidiary cells: the epidermal cells
have straight walls.
[Illustration: Fig. 535. Section of the quarry in the Isle of
Portland in which _Cycadeoidea gigantea_ was found.]
[Illustration: Fig. 536. _Cycadeoidea gigantea._ (The original is in
the British Museum; ⅛ nat. size.)]
[Illustration: Fig. 537. _Cycadeoidea gigantea._ Transverse section
of the stem.]
[Illustration: Fig. 538. _Cycadeoidea micromyela._ A, tracheids from
the stele. B, course of the vascular bundles at the base of a leaf.
C, section of a leaf-trace entering the stele; _m_, _l_, median and
lateral lobes of the trace. (After Lignier.)]
_Cycadeoidea micromyela_ Morière.
This Liassic species from Normandy has been fully investigated by
Lignier[1175]; originally referred to the Conifers, it was afterwards
described by Morière[1176] as _Cycadeoidea micromyela_. As regards
external features the stem is of the usual _Cycadeoidea_ type:
Saporta[1177] assigned it to the genus _Platylepis_. The secondary
xylem consists of tracheids with bordered pits on the radial walls
arranged as single contiguous rows, resembling scalariform pitting, or
as 1–2 rows of separate circular pits (fig. 538, A), a type different
from that of the great majority of Mesozoic species. The uniseriate
medullary rays are 7–20 cells deep, a character recalling the compact
wood of Indian _Williamsonia_ stems. Ramental scales are for the most
part replaced by long unicellular hairs like those of _Williamsonia
scotica_ and some Indian stems. Lignier states that true ramenta
occur on the young leaves and in older fronds become transformed by
separation of the cells into long tubes. Each leaf-trace arises as a
single bundle dividing into three as it leaves the stele and eventually
splits up into several collateral bundles (fig. 538, B, C). The stele
is elliptical. No fertile shoots are preserved: a single axillary
bud is described which agrees very closely with that in _Cycadeoidea
gigantea_.
[Illustration: Fig. 539. _Cycadeoidea Jenneyana_ (?). Longitudinal
section of an ovulate strobilus, showing the pyriform receptacle with
vascular supply, the long interseminal scales and megasporophylls, and
a few of the surrounding bracts. (After Wieland; × 1½ nat. size.)]
_Cycadeoidea Jenneyana_ Ward.
The stems of this species, from the Black Hills of Dakota[1178],
resemble those of _Cycadeoidea gigantea_ and _C. Reichenbachiana_ in
their thick columnar form but differ from the former in the presence
of bisporangiate flowers associated with the leaf-bases. This species
probably reached a length of 3–4 met. A striking feature[1179] is the
unusual thickness of the xylem-cylinder, which shows clear indications
of concentric rings, probably the expression of seasonal changes during
the production of secondary conducting tissue by a single cambium.
Similar concentric rings have been described in the stems of the
recent Cycad _Dioon spinulosum_[1180]. Fig. 539 represents an ovulate
strobilus referred to this species by Wieland.
_Cycadeoidea pumila_ Fliche and Zeiller.
This French Portlandian species[1181] affords a good example of a very
small bulbiform trunk, 3·5–4 by 2·5–3 cm., superficially resembling
a Pine-cone: the leaf-bases are, however, less uniform in size and
shape than Abietineous cone-scales; there are also indications of
interpetiolar ramenta and a small lateral, presumably fertile, branch.
A stem of similar form is described by Saporta[1182] from Corallian
beds in France as _Bulbopodium micromerum_, and _Cycadeoidea nana_
Ward[1183] from Dakota is another example of a small Zamia-like
Mesozoic stem. A small tuberous stem, 8 × 7·5 cm., was described by
Lindley and Button from Lyme Regis as _Cycadeoidea pygmaea_[1184]; no
flowers are shown in the drawing, but occasional irregularities in the
arrangement of the leaf-bases may be due to the presence of lateral
fertile shoots.
=Cycadella.= Ward.
This generic name was instituted by Lester Ward[1185] for some
petrified stems from Jurassic beds in Wyoming of relatively small size,
bulbous or more or less spherical, and characterised by the presence
of a thick layer (5–15 mm.) of dense ramental tissue. The unusually
vigorous development of the ramental scales is an interesting feature,
though it is perhaps questionable whether it is worthy of generic
recognition. The flowers of _Cycadella_, though less than those of most
_Cycadeoidea_ stems, are of the same type. In a later account of the
genus Ward[1186] describes a few additional species and in _Cycadella
ramentosa_ he notes the preservation of young fronds. The fronds are
small and bear a few pinnae: the xylem is said by Wieland[1187] to
be mesarch, but in the absence of more details the foliar bundles
cannot be fully described. In some Cycadellas young flowers, less than
1 cm. in diameter, are preserved, those of _Cycadella wyomingensis_
(7 mm. in diameter) being the smallest bisporangiate strobili so far
recorded. The French species, _Cycadeoidea micromyela_ Mor., resembles
_Cycadella_ in the profuse development of ramental tissue which may
cover the surface of the stem.
=Amphibennettites.= Fliche.
This generic name was instituted[1188] for two species founded on very
imperfectly preserved ‘fruits’ of Lower Cretaceous (Albian) age from
the Argonne which, though in close agreement with _Bennettites_ as
represented by _B. Gibsonianus_ and _B. Morierei_, are referred to a
separate genus on the ground that the preservation is not such as to
establish their generic identity with those species and because of
certain distinctive features.
_Amphibennettites Bleicheri_ Fliche. The ovulate strobili are
sub-elliptical, 3·5 × 3 cm., with several elliptical pits close to
the surface originally occupied by seeds borne on short stalks and
larger than the seeds of other species of _Cycadeoidea (Bennettites)_.
Interseminal scales occur between the seeds. The second species,
_Amphibennettites Renaulti_, is rather larger and more conical: the
seeds reach a length of 11 mm. greater than that of any of the American
seeds described by Wieland. In neither species is there any indication
of an involucre of bracts. The preservation of the specimens leaves
much to be desired, but it would seem that the Argonne fossils agree
in their main characters with Bennettitean strobili and it is doubtful
whether a distinctive generic name is necessary. The occurrence of
seeds over the whole surface, a feature that suggested the name
_Amphibennettites_, may be only apparent and the result of cutting
the cone transversely. It is worthy of note that one of Fliche’s
sections[1189] bears a close resemblance to an Araucarian cone, and in
the absence of structure the two types of cone might easily be confused.
[Illustration: Fig. 540. _Vectia luccombensis._ Transverse section
showing the alternation of fibres, _s_¹, _s_², and radial pairs
of pitted elements, _v_¹ and _v_²; _m_, medullary-ray cells; _a_,
parenchyma cell between four thin-walled elements; _sp_, pits between
adjacent fibres; _l_, much reduced lumen of fibre. (After Stopes.)]
=Vectia.= Stopes. Genus _incertae sedis_.
_Vectia luccombensis_ Stopes.
The generic name _Vectia_ has been given by Dr Stopes[1190] to some
petrified secondary phloem discovered by her at Luccomb Chine in the
Isle of Wight: the fossil is from Aptian beds. The mass of phloem
is 26 mm. in breadth and consists of regularly alternating bands
of thin-walled sieve-tubes and very thick fibres associated with a
little parenchyma (fig. 540). To the naked eye the specimen presents
an appearance suggestive of rings of growth but this is due to the
presence of bands of 2–3 narrow cells which are probably cork. The
whole is penetrated by uniseriate medullary rays. A striking feature
is the regular alternation of single rows of fibres with two bands
of sieve-tubes; in places the two bands of sieve-tubes are separated
by 2–4 rows of very flat, presumably, cork-cells, and similar bands
may be adjacent to or pass obliquely across the fibres. The elongated
elements described as sieve-tubes, though thin in comparison with the
fibres, have thickened walls and on their radial faces are single
rows of circular pits, often in pairs; these are almost certainly
sieve-areas which have lost the finer pitting of the sieve-plates.
The fibres are more or less square in transverse section and have
excessively thick walls, the lumen being reduced to a small hole.
Parenchymatous cells (fig. 540, _a_) occupy the angles between the
sieve-tubes and occasionally stretch tangentially between a pair of
tubes: these are compared by Dr Stopes to companion-cells, but their
manner of occurrence hardly justifies the interesting suggestion that
they may be precursors of the Angiosperm companion-cells. The medullary
rays may be as wide as the elements which they traverse; they are
characterised by their wavy walls, as seen in radial longitudinal
sections; no pitting was noticed. A remarkable feature of the specimen
is its considerable breadth: it is pointed out that in a giant stem
of _Sequoia_ with a girth of over 40 ft the secondary phloem does not
exceed 3–4 mm. in breadth. The great thickness of the phloem in the
fossil suggests comparison with the corresponding tissue in recent and
fossil Cycadean stems, and the alternation of hard and soft phloem is
a feature exhibited also by _Cycadeoidea Gibsoniana_ (fig. 518, B). Dr
Stopes concludes that the phloem is in the main similar to that in some
Cupressineae, Taxineae, and Taxodineae. It is noteworthy that similar
phloem with sieve-tubes and fibres associated with cork is described by
Graf Solms-Laubach[1191] from Upper Jurassic beds in Franz Josef Land.
The systematic position of _Vectia_ cannot be definitely determined,
but I believe that it is more closely allied to Cycadean than to
Coniferous phloem.
* * * * *
+Note.+ It is unfortunate that Mr Wieland’s second volume dealing
with American Cycads [Wieland (16)] did not come into my hands until
nearly the whole of this volume was in type. Students will find in it
many additions to our knowledge of _Cycadeoidea_ and _Williamsonia_,
much theoretical discussion that is suggestive and interesting, useful
summaries of our knowledge of fossil Cycads, and many beautiful
photographic plates illustrating the morphology of American species of
_Cycadeoidea_.