ENDOGENOUS TREES. (Monocotyledons.)
Endogenous trees are those that increase from within. Their elemental parts are similar to those of exogenous trees but the arrangement of such parts differs in that the newer fibres of the Endogen intermingle with the old, pass through a pith-like tissue, and cause cross-surfaces to appear as dotted, whereas the new material of the Exogen is deposited altogether and upon the outside of the old, their sections exhibiting rings or layers. The Palms, Yuccas, Cornstalks, and Bamboos are of the endogens. Bark is unusual on trees of the series.
Endogenous woods are hardest and most compact at circumferences. The stems of palm trees are solid, but those of some of the grasses, particularly those that grow quickly, are hollow.[107] The tube or canal, when existing, is due to sluggishness on the part of the central pith, which, developing more slowly than the outer tissues, finally ruptures and disappears at the center. There are also more or less permanent joints or knots,[108] such as are made familiar by the canes and bamboos. The stems of Endogenous plants are seldom cut up into lumber, but are used in segments, or else entire, as for troughs or piles.[109] The use of Palm wood must be more or less [p184] limited to the neighborhoods in which such trees flourish, but it is probable that the Bamboo can be much more generally employed.
The Endogens include numerous families and many thousand species.[110] The grasses, including wheat, rye, and Indian corn at the North and sugar-cane and bamboo at the South, belong to this group. Most Endogens are herbs; comparatively few furnish material for structural purposes. The Palms, including the palmetto, rattans, cane palms, and others, the Yucca, including the Joshua tree, Spanish bayonet, and others, and the Bamboos, representatives of the grasses, are thus useful. Endogens are also known as Monocotyledons. [p185]
FOOTNOTES
[107] The Bamboo, which is a grass, is hollow, while the cornstalk, which is also a grass, is not.
[108] The knots of endogens correspond to the nodes of exogens. Spaces between the nodes, known as internodes, mark the annual lengthening. Knots are places whence leaves have emerged.
[109] Palm in marine work appears to repel the teredoe. This is probably because of the porous character of the wood. See "Marine Wood Borers," Trans. Am. Soc. C. E., Vol. XL, pages 195 and 204.
[110] Bastin ("College Botany," p. 379) divides into about fifty natural orders distributed among seven divisions. Warming ("Systematic Botany," pp. 277, 278) divides into seven families corresponding with Bastin's seven divisions. A. Gray divides into twenty-one orders or families. Coulter ("Plants," p. 237) divides into forty families, including twenty thousand species.