22

THE PALM-STEM.

mostly to be distinguished from these by their largercavity and somewhat thinner walls, and in the longi-tudinal section by the septum being, at all events in thevicinity of the vascular bundle, horizontal. This thicken-ing occurs sometimes here and there in the outer bundlesof many Palm-stems, e. g. in Kunthia montana, in whichcase it is met with in one vascular bundle and not in theothers; or it is a structure occurring regularly in allbundles, which, however, is only the case in Calamus.Notwithstanding that there is here a great similarityproduced to the liber-cells by the thickening of the walls,they may be distinguished from these by the somewhatthinner walls, a larger cavity, as well as by the circum-stance that, with the exception of the liindermost, theyare elongated in a direction parallel to the wall of thelarge vessel. Their walls, like those of the liber-tubes,consist of several layers, and possess pore-canals, whichare particularly striking in longitudinal sections, sincefrom their small distance from each other, the cell-wallcut through possesses almost a moniliform aspect; andunder these circumstances the nature of these canals, asexcavations perforating the cell-wall down to the outer-most layer, may be recognised most clearly.

The vessels of the Palms must be divided into thelarge and small. Each of these kinds, as is clear fromwhat has been said already, occupies a definite place inthe vascular bundle. The large vessels, traced from thelower fibrous extremity of the vascular bundle to its exitinto the leaf, do not anywhere exhibit the form of thespiral, but that of the scalariform or reticulated vessel.These vessels are composed of rather short tubes, standingone above another. This composition may be perceivedeven by the naked eye in the very wide vessels of Cala-mus Draco, Mauritia vinifera, &c., the length of one ofthe tubes in these plants amounting to T—2 lines. Theface where the ends of the tubes meet one another is veryseldom horizontal, but mostly inclined considerably to-ward the axis of the vessel. As a general rule, the ends