482 DR. ERIC DRABBLE ON THE 
complete continuity owing to a portion of the zone having extended too far peripherally, 
this latter having formed a cylinder on its own account, leaving a gap in the normal ring. 
The excentric cylinder has cleven xylem-groups with two V’s and eleven phloem-groups. 
It gives off a lateral root, and behaves in all respects exactly like an ordinary root- 
cylinder. Below, this structure passes into the normal root-cylinder by a method 
illustrated in Pl. 51. figs. 99 to 102 and fully described above. 
The medullary parenchyma in this region contaius masses of fibrous tissue with 
central vessel or vessels and sometimes also phloem, 
(58) ARECA CONCINNA, Thw. 
The limiting and tegumentary layers are like those in 4. Catechu, L. 
The parenchymatous cortex is without air-spaces, or only with very small ones. In 
this zone occur mucilage containing parenchymatous elements. Small bundles of fibres 
are also present. The endodermis is lignified, and the pericycle one- or two-layered. The 
fibrous zone containing the xylem- and phloem-elements encloses à parenchymatous 
pith with mucilage elements. Xylem V's are occasionally formed. 
In the smaller roots the large internal vessels can be allotted to a single protoxylem- 
group or to a pair of such groups. 
In larger roots the general arrangement is similar, but the xylem-groups are much 
more numerous and the internal large vessels are more scattered. Thyloses are abundant 
in the vessels. 
In still larger roots xylem V's and Y's are abundant, and the xylem arrangement is 
irregular. The large central pith contains five or six fibrous masses, each with one or 
more vessels. 
(56) ARECA sp. 
On the surface is a layer of thin-walled limiting cells, followed by small elongated 
elements. The well-developed parenchymatous cortex is provided with strands of fibres 
and small scantily developed air-spaces. The endodermis is non- lignified and the 
pericycle is one-layered. The fibrous zone consists of wedges of tissue completely or 
nearly completely separated from one another by radiating extensions of medullary 
parenchyma. These wedges contain the xylem, usually one xylem-group to each wedge 
The phloem-bundles may lie laterally in the fibrous wedges or in the parenchymatous 
tissue hetween them. 
On one side there is a more distinct break in the fibrous ring, and here the incurved 
edges carry phloem-bundles internally. The endodermis is slightly inflected, but is 
continuous over the gap. At such a point there is a tendenc sy for the fibrous wedges to 
become free medullary strands. More proximally the central cylinder is broken up into 
ares, and into the gap between each pair the endodermis dipsin and is discontinuous. At 
these gaps some of the wedges are present as free medullary strands, and in the general 
. medullary parenchyma are developing masses of fibres enclosing one or more vessels, and 
sometimes also a little phloem. Bundles of fibres similar to those of the cortex are 
also present. 
Small and regular air-spaces occur in the cortex of these large roots. 
