This Division embraces three classes: Cycadeæ, Coniferæ, And Gneteæ. It is no doubt monophyletic, and has taken its origin from heterosporous Ferns, now extinct, most nearly related to the Ophioglossaceæ and Marattiaceæ. The Cycadeæ appear to be the oldest class. The Coniferæ are related to these through Ginkgo. The Gnetaceæ are more isolated. The Division is not continued into the higher Flowering-plants; it has evidently attained its highest development, and is now in a retrograde condition. The similarity which has often been pointed out between certain Coniferæ and Lycopodinæ is only in analogous resemblances, and does not entitle one to suppose that there is a nearer relationship, or that the former take their origin from the latter.
Class 1. Cycadeæ.
The stem is very rarely ramified. The leaves are large, pinnate, and arranged spirally. The flowers are diœcious, without perianth.
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.
Fig. 257.—Cycas circinalis. Part of a young leaf with circinate leaflets.
