THE STEM is frequently a corm, bulb, or other variety of underground stem, as the majority of the Monocotyledons are perennial, herbaceous plants; it has scattered, closed vascular bundles (Fig. 276), and no cambium by which a continuous thickening may take place. The stem of the Palms, however, attains a very considerable thickness, which is due to the meristem of its growing-point continually increasing in diameter for a lengthened period (often for many years), until it has reached a certain size. In this condition the growing-point has the form of an inverted cone, and it is only when this cone has attained its requisite size that the formation of a vertical cylindrical stem commences. Certain tree-like Liliaceæ, as _Dracæna_, _Aloe_, etc., have a continuous increase in thickness; this is due to a meristematic layer, which arises in the cortex, outside the original vascular bundles, which were formed at the growing-point of the stem. This meristem continues to form thick-walled parenchyma and new, scattered vascular bundles. The primary vascular bundles, in the Palms and others, run in a curved line from their entrance into the stem at the base of the leaf, towards the centre of the stem, and then bend outwards and proceed downwards in a direction more parallel to the sides of the stem (Fig. 277). The bundles formed later, in those stems which increase in thickness, are not continued into the leaves. THE BRANCHING as a rule is very slight, the axillary buds of the majority of the leaves never attaining development, _e.g._ in the Palms, bulbous plants and others. As the cotyledon arises singly, the succeeding leaves also must be scattered, but they are frequently arranged in two rows (Grasses, Iris, etc). _The first leaf borne on a branch_ (the “Fore-leaf,”[24]--the bracteole, if on a floral shoot) has generally, in the Monocotyledons, a characteristic form and position, being situated on the posterior side of its own shoot, and hence turned towards the main axis; it is sometimes provided with two laterally-placed keels (Figs. 279 _f_, 290 _øi_), but the midrib is often absent. It arises in some cases from two primordia, which at the beginning are quite distinct, and thus has been regarded as formed by two leaves. It is, however, only one leaf, a fact which is evident from several circumstances, one being that it never supports more than one shoot, and this stands in the median plane (Fig. 279). [Illustration: FIG. 276.--Transverse section of the stem of a Palm: _v v_ is the wood portion, _b b_ the bast portion of the vascular bundled.] [Illustration: FIG. 277.--Diagrammatic representation of the course of the vascular bundles, from the stem into the leaves in a Monocotyledon.]