ANATOMY OF THE ROOTS OF PALMS. 437 
whose walls give lignin-reactions—may undergo specialization in one of two directions :— 
(1) The walls may become thickened and pitted, the extreme form being a densely 
sclerosed stone-cell, or (2) elongation of the cell may take place, leading to the appearance 
of individual, comparatively thin-walled fibres scattered irregularly throughout the paren- 
chymatous cortex. Fibres of this typeare often collected into bundles—the Kentia-ty pe 
of the foregoing description. In other eases the fibres are greatly extended and their 
walls considerably thickened with consequent reduction of the lumina. This latter type 
of fibre—the so-called Raphia-type—usually occurs in bundles, accompanied externally 
by small erystal-containing sacs, or stegmata. 
Mucilage-sacs and Raphides-containing Elements, 
The cells of the tegumentary layers frequently contain dark-coloured mueilage. 
Occasionally definite thick-walled mucilage-reservoirs containing raphides are also present 
in this zone, as in Caryota sp. (Pl. 49. fig. 42). 
Individual mucilage-cells may also be scattered throughout the cortex and pith. 
Specially developed elements containing bundles of raphides composed of calcium 
oxalate embedded in mucilage are regularly formed at the apex. These first appear as 
elongated cells in the cortical or medullary parenchyma, in which bundles of raphides 
develop, occupying nearly the whole lumen of the cell, the protoplasm and nucleus being 
relegated to one, usually the upper, end (PI. 49. fig. 38). | 
These cells are arranged in rows, and keep pace in growth with the longitudinal 
extension of the stem, but do not undergo any division. Hence very considerably 
elongated elements result. The contents of these cells become very mucilaginous 
(Pl. 49. figs. 38, 39, & 40), and the nucleus appears to fragment (Pl. 49. fig. 40) and 
finally disappears. These elements are usually very abundant and well developed in tlie 
younger portion of the root, but become more or less obliterated in the older portious. 
Hanstein (20) discussed the question as to whether the mucilage-spaces in Mono- 
cotyledons are formed by the fusion of more than one element by the disappearance of 
transverse walls, and from his study of Commelina concluded that such is the case— 
raphide-containing vessels resulting. 
De Bary (6) was unable to substantiate this. He found, however, that the transverse 
walls might become perforated by the absorption of water and consequent swelling of 
the mucilage during the preparation of sections, and suggested that this might also oceur 
in nature. De Bary's conclusion that absorption of transverse walls does not take place 
is entirely borne out by an examination of the roots of Palms. Here the erystal-sacs just 
behind the apex are nearly filled with raphides (Pl. 49. fig. 38). About half an inch 
behind the apex the cells have grown considerably in length, as have also the crystals 
themselves, but the transverse walls are still as definitely present as in the first case, no 
signs of any disappearing walls being seen (Pl. 49. fig. 39). Inthe older regions of the 
root the crystal-sacs have increased still further in length, and the bundles of raphides 
are very short in proportion to the length of the containing element (PI. 49. fig. 40). If 
the long erystal-sae had been formed by cell-fusions several bundles of raphides should 
occur. Such is, however, not the case, and itis concluded that longitudinal fusion of cells 
9R2 
