By the unequal development of the secondary cortex the stem becomes twoor three-lobed; the roots, which branch dichotomously, spring from the furrows between the lobes.
In the Metanemertini, where the longitudinal stems lie inside the muscular body-wall, definite and metamerically placed nerve branches spring from them and divide dichotomously in the different tissues they innervate.
The Carboniferous forerunners of the tiny club-moss were then great trees with dichotomously branching stems and crowded linear leaves, such as Lepidodendron (with its fruit cone called Lepidostrobus), Halonia, Lepidophloios and Sigillaria, the largest plants of the period, with trunks sometimes 5 ft.
The diarch roots of a Sphenophyllum have been described by Renault, who has also investigated the leaves; they were strongly constructed mechanically, and traversed by slender vascular bundles branching dichotomously.
The leaves are highly compound, dividing dichotomously into several leaflets, each of which is deeply pinnatifid, with fine segments.
