448 DR. ERIC DRABBLE ON THE 
having apparently entered into the peripheralring—a very uncommon occurrence. One 
of the strands composing the ring of arcs persists as a radially symmetrical cylinder. 
A similar thing occurs in another section of Kentia sp. (Pl. 50. fig. 59). 
Dypsis madagascarensis (Pl. 50. fig. 58) shows much the same structure, but here 
medullary strands occur and the lateral fusion of the ares is more extensive. An 
interesting peculiarity is evident in the small medullary strand a. It approximates very 
closely to the periphery of the ring, abutting on a gap between two arcs. ‘This small 
strand is on its outer face provided with endodermal cells exactly like those outside the 
ares. In this root also one peripheral strand retains its radial symmetry. 
In Areca sp. (Pl. 50. fig. 60) the fusion of the ares is much more extensive on one 
side of the root than on the other. The elements of the xylem-groups are more 
abundant than usual, and in some cases the larger internal vessels of the metaxylem are 
accompanied internally by smaller vessels which represent persistent traces of the 
internally directed xylem-groups of the radially symmetrical strands, the protoxylem of 
which has disappeared. A strand possessing two protoxylem-groups, one directed 
externally and one internally, is united with the inner extremity of a fibrous wedge of 
the peripheral system. A similar strand is found in Cocos plumosa (Pl. 50. fig. 61), but 
here the vascular elements are reduced to a single vessel as they are in most of the 
medullary strands. In one, however, the radial arrangement of four xylem-groups and 
four phloem-groups persists. The peripheral system forms aring only incomplete on the 
adaxial side, and in the gap occurs a small strand like the one just described, but 
possessing five xylem- and phloem-groups. 
Cyrtostachys Renda (Pl. 50. fig. 62) is of particular interest in retaining two of the 
internally directed xylem-groups of the original strands, accompanied by phloem laterally, 
and a third group of two vessels in another wedge representing the metaxylem-vessels 
of such a group whose protoxylem-elements have disappeared. 
In the section of Dypsis madagascarensis (Pl. 50. fig. 63) the ring is only incomplete 
on the adaxial side. The wedges bounding the gap alone show internal phloem, and in 
one case internally directed protoxylem also. 
In Licuala gracilis (Pl. 50. fig. 64) the ring is complete. In several cases the large 
metaxylem-elements are accompanied centrally by remains of the internally directed 
xylem, and in other cases a well-developed internal xylem-group persists. The three 
medullary strands show three stages in the normal reduction of these structures. One 
possesses a central vessel and two radiating protoxylem-groups. The second has lost its 
protoxylem, and the third only retains a single central vessel. Thus the fact that these 
medullary strands, which possess, as is usually the case, only a single central vessel, really 
represent reduced structures which had originally a radial arrangement of xylem, is here 
well illustrated, as is also the further fact that some of the large internally placed vessels 
of the fibrous zone are the metaxylem-elements of internally orientated xylem-bundles 
. whose protoxylem has disappeared. 
‘The rich development of metaxylem and its tangential extension in P/ychosperma 
filifera (Pl. 50. fig. 65) have been already described, as has also the abundant 
V-formation in Livistona australis (Pl. 50. fig. 66). It may here be noted that 
