48 THE PALM-ROOT. 



respect to the epoch of their development, the latter agree 

 with the spiral vessels of the vascular bundle of the stem, 

 for they are already completely formed at a time when 

 the large vessels still appear as thin -walled tubes without 

 fibrous deposits, and the cells of the root have yet but 

 extremely delicate membranes. The vessels are sur- 

 rounded by rather thick-walled, much elongated cells, 

 with horizontal septa. But only those cells situated next 

 to the vessels exhibit these horizontal septa, and they pass, 

 in the interspaces between the vessels and in the central 

 space inclosed by the vessels, into prosenchymatous cells, 

 which, in the centre of the vascular bundle, are again 

 transformed into elongated parenchyma, and form an 

 analogue to the pith. The whole central body is sur- 

 rounded at its circumference by a few layers of thin- walled 

 prosenchymatous cells, to which follows a row of narrow, 

 elongated thick- walled cells. 



Between every two groups of vessels lies a bundle of 

 proper vessels ; the size of this is ruled by the length of 

 the rows of vessels lying beside it, for only a small roundish 

 bundle lies between the short rows, while those situated 

 between the long rows extend far in toward the centre of 

 the root. The arrangement of the proper vessels is always 

 such, that those lying internally are very wide, the outer 

 very narrow : the narrower and wider are not, as in the 

 stem, mingled together. The membranes of these vessels 

 are always thin, not unfrequently finely porous, which 

 also sometimes occurs in those of the stem of Tamus 

 elepliantipes. They are composed, both the wide and 

 narrow, of closed elongated tubes, with horizontal or 

 diagonal septa; like those of the stem, they contain an 

 opaque, granular sap. 



The cortical substance consists chiefly of regular thin- 

 walled parenchyma-cells, with intercellular passages. 

 Those cells in the vicinity of the vascular bundle have no 

 intercellular passages between them, and are somewhat 

 expanded in the direction of their breadth. The inter- 

 cellular passages also disappear toward the surface of the 



