4.58 DR. ERIC DRABBLE ON THE 
The endodermis is of the usual lignified type. 
The pericycle is two cell-layers in thickness. 
The sclerenchymatous zone is well developed and composed of densely lignified and 
thickened elements. In the centre is a parenchymatous pith. 
The sclerenchymatous ring is lobed internally, rays of the pith extending in an outward 
direction between the wedge-shaped lobes of sclerenchyma. There is only one irregular 
ring of large vessels, and these are placed very peripherally. They are fewer in number 
than the protoxylem-groups, and hence V-formation is general. 
(6) THRINAX PARVIFLORA, Sw. 
In the young root the limiting-layer is lignified, as are also the subperipheral layers 
of elongated cells, these latter being also slightly cuticularized. The greater part of 
the cortex consists of ordinary parenchyma with no fibres. There are very large, radially 
extended air-spaces, with occasionally a thin tangential diaphragm of cells. These 
cavities extend to within ene or two cells of the endodermis. The endodermal cells are 
lignified and “ fibrously thickened ” on all but the outer tangential walls. The pericycle 
is generally only one cell in thickness, and is followed by the broad sclerenchymatous 
zone in which the xylem-vessels and the phloem are embedded. 
The vessels of the protoxylem are lignified, but the larger internal vessels are not. 
These latter vessels do not extend far centrally. V's are formed embracing the phloem. 
In the centre is a small parenchymatous pith. 
The older roots are extremely hard, lignification being very extensive and the elements 
very small and closely packed. The outer portion of the cortex is made up of elongated 
elements with almost totally occluded lumina, with irregular radial rows of thinner- 
walled elements, along which the sections invariably split in cutting. This zone is 
succeeded by a parenchymatous cortex with very irregular air-spaces and a large 
proportion of lignified, thick-walled, pitted parenchyma. The endodermic cells are 
greatly thickened and lignified on all the walls. The pericycle is lignified and is two 
cells in thickness. 
The sclerenchyma enclosing the xylem- and phloem-elements is greatly sclerozed and 
pitted. There is no pith, but in many cases the centre of the root is occupied by a 
cavity, the walls of which are blackened as though diseased. "The xylem-plates extend a 
considerable distance centrally, and occasionally a V is formed. All the vessels are 
lignified. 
The phloem-bundles show considerable radial extension. 
(7) THRINAX EXCELsA, Lodd. 
_ A distal portion of the root shows a limiting-layer of thin-walled lignified cells, nearly 
exfoliated. Underneath this are many layers of somewhat lignified, elongated cells. 
The parenehymatous i inner cortex has irregular air-spaces and lignified, fibrous, pitted 
celis. The innermost portion of the cortex is made up of smaller, more tightly packed 
cells, without See but with many lignified fibres. The endodermis is lignified, and 
i SER idis. i: SED SS RE 
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