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.