The stem is very _rarely ramified_. The leaves are _large_, _pinnate_,
and arranged spirally. The flowers are _diœcious, without perianth_.
[Illustration: FIG. 256.--_Cycas circinalis_ (female plant). The
carpels are seen hanging from the top of the stem. Three leaves
with the leaflets still rolled up project almost vertically into
the air, from the centre of the crown.]
There is only one order, the =Cycadaceæ=.--In habit they resemble the
Ferns, especially the Tree-Ferns (compare Figs. 207 and 256). The stem
is tubercular (Fig. 258), or cylindrical (Fig. 256), but not very tall
(as much as about 12 metres), and very rarely ramified. [In Ceylon,
unbranched specimens of _Cycas_ are rarely met with in the wild state.
The stems of _C. circinalis_ occasionally branch in greenhouses.]
The LEAVES are arranged spirally, and so closely together that no
free stem-surface is left between them, and have only a slight sheath
(which is not amplexicaul, as in the Palms). They are compound (most
frequently pinnate; in _Bowenia_, bipinnate); in some genera the leaves
are rolled up in various ways, resembling the vernation in Ferns (Fig.
257); they are leathery and perennial. In some, stipules are present,
as in the Marattiaceæ. Groups of scale-leaves alternate in the majority
with groups of foliage-leaves.
[Illustration: FIG. 257.--_Cycas circinalis._ Part of a young
leaf with circinate leaflets.]
[Illustration: FIG. 258.--A male plant of _Stangeria paradoxa_
(about 1/15 nat. size).]
[Illustration: FIG. 259.--Female cone of _Zamia integrifolia_
(½-⅓ nat. size). The male cone is very similar externally.]
The FLOWERS are without perianth. The MALE FLOWER is sometimes an
enormous collection of stamens (Fig. 258), which are flat in some
(_Cycas_, Fig. 241), shield-like in others (_Zamia_, _Ceratozamia_)
like the sporophylls in Horsetail (Fig. 259); but in all, the
pollen-sacs are situated in large and varying numbers on the back of
the stamens, and arranged in groups of 2–5, like the sporangia in the
sori of the Ferns (Fig. 241 _b_, _c_). FEMALE FLOWERS _are wanting_ in
_Cycas_, because the carpels do not terminate the apical growth of the
stem. After a group of foliage-and of scale-leaves, a group of carpels
is developed, which are pinnate and resemble the foliage-leaves,
bearing on their edges a number of ovules (most frequently 5–6)
(Figs. 245, 256); the same stem produces successively scale-leaves,
foliage-leaves, and carpels. The differentiation is not much more
advanced than in certain Ferns (_Struthiopteris_, _Blechnum_), where
barren and fertile leaves of different form regularly alternate. _The
other genera have female flowers_; the carpels are shield-like in
_Zamia_ and _Ceratozamia_ (Fig. 246), and collected into cone-like
flowers, which terminate the growth of the stem (Fig. 259). The number
of ovules in these instances is two to each carpel.
The SEEDS are large (most frequently 2–6 centimetres long) and
plum-like; the external layer of the testa is fleshy, while the
internal one is hard and horny. There are two systems of vascular
bundles in the testa, one outside, the other inside the stone. The
embryo is straight, attached to the end of the suspensor, which is
often long, filamentous, and rolled up; it has one or two cotyledons.
The embryo in _Ceratozamia_ and others is very slightly
developed, at the time when the ripe seed is detached from
the carpel; and it is not until after sowing that its further
development and germination proceed. This calls to mind the
Cryptogams, especially _Selaginella_, whose macrospores are
thrown off filled with endosperm; but the oosphere is not
fertilised till after the separation of the macrospore from the
parent-plant, while in the Cycadeæ fertilisation is effected
before the separation. In _Cycas_ the testa may rupture, and
the endosperm grow and become green in the light, even though
no embryo has been formed. This also is an indication of its
prothalloid nature.
Gum-passages are present in all organs. Collateral vascular
bundles, with spiral and scalariform tracheides, are found;
and normal thickening takes place by means of a cambium.
An exceptional mode of growth is found in _Cycas_ and
_Encephalartos_, the cambium ceases to divide after a time
and is replaced by a new cambium which arises in the cortical
parenchyma just outside the bast, and which forms a new ring
of xylem and phlœem. This may be repeated so that a number of
concentric rings are produced. In _Ceratozamia_, structures
resembling corals extend from the roots in a vertical direction
and appear on the surface of the soil; these are peculiar roots,
in which a symbiotic Alga (_Anabæna_) is found.
The Cycadeæ were formerly (from the Coal period to the Later
Cretaceous) far more numerous than at the present day. They
appear to have been most numerous in the Trias and Jurassic.
The remnant (75 species) which have persisted to the present
time are found in all tropical countries. _Cycas_ (Trop. and
Sub-trop., Eastern Hemisphere); _Dioon_ (Mexico); _Macrozamia_
(Australia); _Encephalartos_ (Trop. and S. Africa); _Stangeria_
(Fig. 258, Sub-trop. South and East Africa); _Bowenia_ (Trop.
Australia); _Ceratozamia_ (Mexico, New Granada, Western Brazil);
_Microcycas_ (Cuba); _Zamia_ (Trop. and Sub-trop. N. America.)
USES. Sago is made from the starch-containing pith of _Cycas
revoluta_ and _circinalis_. The leaves are often used at
funerals and church festivals, under the name of “palm-branches.”
Class 2. =Coniferæ= (=Pine-trees=).
The stem _branches freely_. The leaves are _entire_, relatively small,
linear or reduced to scales. The flowers are without perianth. The
ovules naked. It is seldom that the female flower is reduced to only
one carpel.
Whilst the Cycadeæ principally resemble the Ferns, the Conifers partly
resemble the Lycopods, and partly the Equisetums--the former especially
in the _needle- or scale-like_, leathery, simple, and often perennial
leaves (“evergreen plants”), which _never possess stipules_ (Figs. 263,
270, 272). _Ginkgo_ deviates from this, being no doubt the oldest,
and the Conifer which stands nearest to the Cycadeæ (Fig. 260). The
resemblance to the Equisetums is especially owing to the fact that
the stem ramifies abundantly, and often very regularly, forming a
pyramid with verticillate branches. In addition to the foliage-leaves,
scale-leaves (bud-scales) are present in the majority of species.
The FLOWERS are monœcious or more rarely diœcious. _Perianth is
wanting._ The stamens of the _catkin-like male flowers_ (Fig. 267,
_J_) are of different forms, but as a rule more or less shield-like.
As in the Cycadeæ, the pollen-sacs are in all cases situated _on the
underside_. There are, as a rule, two pollen-sacs (the Abietaceæ, Fig.
267), or 3–5, (the Cupressaceæ and Taxaceæ, Fig. 243); a few have more,
_e.g. Araucaria_ (Fig. 242); they dehisce by clefts.
If, in commencing our consideration of the _female flower_, we begin
with that of _Ginkgo_, we shall observe in the corner of a scale-
or foliage-leaf a small flower, which consists of two carpels, each
bearing one ovule, and reduced almost to the ovule itself (Fig. 260
_C_, _D_). The flower in _Podocarpus_ is still further reduced, viz.
to a single carpel with one ovule, which is anatropous and has two
integuments. This ovule is situated in the axil of a cover-scale (_c_,
in Fig. 262 _D_), and several female flowers of this description are
collected in a small cone, the stalk and bracts of which become fleshy
(Fig. 262 _C_). The external integument also becomes fleshy (an aril).
_Dacrydium_, which is clearly related to _Podocarpus_, has an external
integument which developes more independently as a fleshy aril (Fig.
262 _B_, _B’_). _Microcachrys_ also is clearly allied to these: the
bracts are more fleshy, and the ovule (_i.e._ the female flower) is
protruded beyond the bract (Fig. 262 _A_, _A’_). _Taxus_ stands in a
more isolated position: a flower which has been reduced to an ovule is
situated, in this instance, on the apex of a secondary branch which is
studded with floral-leaves (Figs. 263, 264); an external integument
is developed on all sides and surrounds the seed as a scarlet aril.
According to this conception _the aril corresponds to an external
integument_, and the Taxoideæ thus possess a partly dichlamydeous
ovule. Only _Ginkgo_ and _Cephalotaxus_ appear to deviate from this,
as in these there is only one integument (unless the small outgrowth
indicated by _ar_, in Fig. 260 _D_, really is a rudimentary, external
integument); in CYCADEÆ, to which _Ginkgo_ is most closely related,
there is likewise only one integument. But in these genera the testa
is differentiated into two layers, and the seed resembles a drupe; like
the Cycadeæ there is an external fleshy covering and an internal hard
one, and these two layers may probably be considered homologous with
the two integuments. This theory is also borne out by the arrangement
of the vascular bundles in _Cephalotaxus_ and _Podocarpus_, which
present the xylem in the fleshy external layer to the _outside_ of the
testa, which is therefore the upper side of the integument (Celakovsky).
The coalescence of the integuments into one is only slight in
_Torreya_, more pronounced in _Podocarpus_ and strongest in
_Cephalotaxus_ and _Ginkgo_. Celakovsky terms these ovules
“holochlamydeous.”
If we pass from these to the order PINOIDEÆ, we find the female flowers
collected into catkin-like cones, which have been considered from
various points of view to be sometimes single flowers, at other times
compound inflorescences. The structure in ABIETACEÆ is as follows: a
number of spirally arranged, scale-like leaves, _cover-scales_ (Figs.
267, 268), are situated on a long axis. In the axil of each cover-scale
a larger leaf-like projection, _the ovuliferous scale_, is borne,
which turns the upper side towards its cover-scale (which is shown by
the fact that the wood of its vascular bundles is turned downwards
and towards the wood in the bundles of the cover-scale: Fig. 269).
Two ovules, with micropyles turned towards the central axis, and with
apparently only one integument (Fig. 268), are situated on the dorsal
side of each ovuliferous scale, _i.e._ the side turned away from the
cover-scale. The ovuliferous scales grow after fertilisation, into the
woody or leathery “cone-scales,” which are usually much larger than the
cover-scales. This ovuliferous scale with its axis may, according to
Celakovsky, be considered as a dwarf-branch which is situated in the
axil of the cover-scale, and bears two ovules (in the same way as in
_Ginkgo_, one long-stalked flower, reduced to two ovules, is situated
in the axil of a leaf), and _in this case the external integument of
the ovules_ is expanded into leaf-like bodies, which have united to
form one “_symphyllodium_” (_ovuliferous scale_) which is inverted
so that its dorsal side is turned upwards and bears the nucellus and
the other integument (“hemichlamydeous” ovules). The carpel itself
is therefore in this instance extremely reduced. The keel, or (in
_Pinus_) “mucro” (Fig. 268 _B_), which is found in several genera,
represents then a third carpel, which is sterile. In the other orders
of the Pinoideæ the cover-scales and ovuliferous scales grow more and
more together and finally form one structure, which also is termed a
“cone-scale,” although from its development it cannot be homologous
with the cone-scales of the Abietaceæ. This connation is least in the
TAXODIACEÆ and ARAUCARIACEÆ and may be traced on the upper surface
of the “cone-scale” by the presence of a stronger or slighter ridge
or pad, the free portion of the ovuliferous scale (Figs. 256, 266,
269). It is most strongly pronounced in the CUPRESSACEÆ, in which the
two scales form one single structure, the cone-scale (Fig. 274). The
vascular bundles in the under portion corresponding to the cover-scale,
have the xylem towards the upper side as usual in leaves, whilst
the bundles present in the upper side of the cone-scale, which thus
represents the ovuliferous scale, turn their xylem downwards. The
hemichlamydeous ovules are then situated on the upper side of this
cone-scale. According to this theory the CUPRESSACEÆ appear to be
the youngest type, a view which corresponds with their vegetative
structure. If there is only one ovule in these orders as in _Agathis_
(Fig. 265) and _Araucaria_, then the flower is reduced to a single
carpel and one ovule, as in the case of _Dacrydium_ and _Microcachrys_.
If two or more ovules are present, then the same number of carpels may
be supposed to exist, the external integuments of their ovules being
developed into leaf-like structures which collaterally coalesce to form
a “symphyllodium,” or are suppressed.
According to this theory, which is based on the researches of
Celakovsky, the female flowers of the Coniferæ may be classed thus:--
1. In all cases situated in the axil of a bract and collected into
cones, with numerous flowers or with few or one flower. In _Ginkgo_
only, are they situated in the axil of foliage- or scale-leaves.