The second division of the vegetable kingdom are the Endogenæ, which are those plants growing from a central bud only, as the palms, bamboos, and canes of all kinds, the grasses and all graminiferous or grain-bearing plants, as wheat, barley, &c. They have but one cotyledon in the seed and have no bark, but in place thereof a kind of natural varnish or thin coating of silica; this varnish or external polish is seen in the stalks of corn and on canes. Their leaves are often of great size, the veins run parallel to each other (fig. 8), they often grow from an expanded base which surrounds the stalk as in corn, and branch off at regular intervals making knobs or joints, as may be seen in the bamboo cane (figs. 9 and 10), in other cases they branch off spirally, and when fallen form a sort of trellis-work on the stem (as in some of the palms) but always in a regular manner. The wood of this family of vegetables has the same porous structure as cane (figs. 11, 12, 13,14), and is often hollow in the centre, becoming more and more solid according to the age of the tree. The stems of these plants are limited in growth and soon acquire their full size, which never exceeds eighteen or twenty inches in diameter although some of the palms are nearly 150 feet high. When the stem has acquired its full size, the continual production of more woody fibres makes it impossible that these (like the exogenæ) can have a very extended period of existence, for when every part of the stem is full of woody matter, the plant ceases to grow from obstruction to the circulation of the juices. The stems of some of this family are always hollow like the stalks of corn; this arrangement allows of great elevations without bending, and is found to be the form which gives the greatest strength from a given quantity of material--one of those beautiful mechanical perfections of nature which man first admired and then endeavoured to imitate. [Illustration: FIG. 8.--ENDOGENOUS LEAF, SHOWING PARALLEL VENATION.] [Illustration: FIG. 9.--BAMBOO CANE, SHOWING JOINT.] [Illustration: FIG. 10.--BAMBOO CANE, SPLIT OPEN.] [Illustration: FIG. 11.--PERPENDICULAR SECTION OF ENDOGENOUS WOOD.] [Illustration: FIG. 12.--PART OF THE SAME, MAGNIFIED.] [Illustration: FIG. 13.--TRANSVERSE SECTION OF ENDOGENOUS WOOD.] [Illustration: FIG. 14.--PART OF THE SAME, MAGNIFIED.]