ANATOMY OF THE ROOTS OF PALMS. 463 
generally two-layered, but opposite the phloem it becomes three-layered. The cells are 
non-lignified, but the cellulose walls are thickened in a scalariform manner. The 
sclerenchyma in which the xylem and phloem lie extends to the centre of the root. 
The protoxylem- and the phloem-groups run in the periphery. More internally there is 
a single ring of large vessels. In some cases one of these forms the apex of a V, the 
arms of which are formed by two protoxylem-groups. 
Towards the centre of the root are two bands of parenchyma separated by a broad 
sclerenchymatous mass enclosing two large vessels. This band represents the medullary 
sclerenchymatous strands of many other palm-roots. 
In another root a definite parenchymatous pith without sclerenchymatous strands but 
with air-spaces and some lignified cells occurs. 
(18) SABAL ADANSONI, Guerns. 
The limiting-layer is composed of thin-walled isodiametrie cells with dark contents 
and slight lignification of the walls. Then follows a zone of parenchymatous elements, 
the outer members and a few of the innermost of which are lignified, lignification 
proceeding centripetally and centrifugally. The inner cortex is parenchymatous, the 
middle region being composed of longitudinal diaphragms of cells separating large 
radially arranged air-spaces. In this region also occur elongated, lignified, and pitted 
elements, but no fibres. The innermost zone consists of smaller cells and some lignified 
elements, but no air-spaces. The endodermis is similar to that in S. glaucescens. The 
pericycle is only one cell in thickness, except opposite the phloem, where it becomes two 
cells in thickness. It is lignified and pitted. The sclerenchymatous zone extends nearly 
to the centre of the root and carries peripherally the protoxylem and the phloem. There 
is a single ring of large internal vessels; occasionally this ring is doubled locally. 
Centrally a parenchymatous pith occurs, having in its midst a large air-space formed by 
disintegration of parenchymatous elements. 
(19) SABAL PALMETTO, Lodd. 
The slightly lignified limiting-layer is succeeded by a prosenchymatous zone, of which 
the outermost elements alone are lignified. This zone passes gradually into a large- 
celled parenchymatous cortex with large radially extending air-spaces and without 
fibrous bundles or individual lignified elements. The innermost layers of the cortex 
are composed of smaller-celled. parenchyma without air-spaces. This layer is 
incompletely separated from the main body of the cortex by an irregular zone of 
lignified pitted elements similar to those scattered irregularly throughout the cortex of 
many other species. The endodermic cells are thin-walled, non-lignified, and non- 
cuticularized. The pericycle is generally three cell-layers in thickness, except opposite 
the protoxylem, where only two layers may be present. The pericyclic ceils have thin 
cellulose walls. 
The xylem and phloem are embedded in non-lignified prosenchyma and | parenchyma. 
The innermost prosenchyma of this zone alone is lignified. The outermost protoxylem- 
