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.
2. It is only in Taxus that bracteoles are present.
3. They are formed only from rudimentary carpels, in which the stem takes no part.