Fig. 258.—A male plant of Stangeria paradoxa (about 1/15 nat. size).
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.”