ANATOMY OF THE ROOTS OF PALMS. 449 
V-formation is now explicable as due to the persistence of two of the radiating xylem- 
groups of the original strand instead of the one which usvally alone persists. 
Double V-formation, such as obtains in Heterospathe elata (Pl. 50. fig. 69), is entirely 
explicable in the same way. Thus in the group on the left of the figure we are probably 
dealing with four xylem-groups, two of which had originally had an internal orientation, 
but which became outwardly directed when fusion of the strand into the peripheral ring 
occurred. That such an alteration in orientation may occur has been already observed 
for Kentia, where the outward orientation of two xylem-groups becomes reversed on 
fusion of the strand with the peripheral are (p. 446, figs. 1 & 2). 
The interest of the sections of Sabal glaucescens (Pl. 50. fig. 67) and Phenix 
dactylifera (Pl. 50. fig. 68) attaches chiefly to the medullary strands, which have 
already received attention. 
In Corypha umbraculifera (Pl. 50. fig. 70) the internal vessels are extremely large 
and occupy almost the whole of the centre of the root, no pith being present. 
The same condition is found in Raphia Hookeri (Pl. 50. fig. 71), but to a less extent. 
These large internal vessels almost certainly represent the metaxylem-elements of the 
central strands whose protoxylem has disappeared and are thus comparable with the 
large vessels of the medullary strands of most roots. 
In Latania Commersonii (Pl. 50. fig. 72) a similar abundant development of large 
vessels occurs, but a central pith is here present. A further point of great interest lies 
in the fact that phloem-groups of the internal strands have here persisted, and 
appear as phloem-bundles scattered throughout the fibrous zone amongst the large 
internal vessels. 
‘In Phenix sylvestris (Pl. 50. fig. 73) the internal vessels are reduced to a single ring, 
while in Sabal filamentosa (Pl. 50. fig. 74) no vessels occur which cannot with con- 
siderable certainty be allotted to the same original strands as those to which the 
protoxylem-groups belong, while this is still further evident in the perfectly normal 
root of Kentia Forsteriana (fig. 75). 
In Pl. 50. figs. 77 to 88 a diagrammatic résumé of the changes which take place in 
the root is presented. ! 
In Pl. 50. fig. 77 the series of cylinders each with a number of exarch xylem-groups 
is seen scattered throughout the ground-parenchyma of the base of the root. Each 
cylinder shows a root-like structure with alternating xylem- and phloem-groups. 
In Pl. 50. fig. 78 fusion of the peripheral cylinders has commenced, and in Pl. 50. 
fig. 79 reduction of the internally directed xylem-groups has set in, with disappearance 
of internal phloem. i j 
The protoxylem-elements of the bundles in the medullary strands which are formed 
by those cylinders which do not enter into the peripheral system have aborted, but the 
ill persists. 
PAL "i 80 the fusion is incomplete only at one point, and the internal xylem 
is represented only by the large metaxylem-elements. Reduction of the xylem and 
phloem of the medullary strands has progressed still further than in Pl. 50. fig. 79. 
In Pl. 50. fig. 81 the peripheral ring is complete, and shows only a depression on one 
