ANATOMY OF THE ROOTS OF PALMS. 441 
fig. 50), where the development was traced and was found to follow the normal course, 
the surrounding parenchyma extending into the lumen of the vessel through the 
pits, and presenting the appearance of small rounded globules projecting freely ; these 
are then eut off by a wall and undergo division, finally filling the vessel with a 
parenehymatous tissue, which may later become lignified and pitted. 
The development of the vessels was traced in Kentia sp. and in Areca sp. They first 
appear as longitudinal rows of cells in the apex, a short distance behind the meristematic 
group. Each cell is of considerable diameter as compared with the surrounding 
elements, but is very shallow. Each is richly provided with protoplasm and has a large 
nucleus. Further back the individual elements of the strand are much elongated and 
the nucleus is beginning to disappear, while still further up the root the nucleus has 
quite gone, and the disintegrating protoplasmic contents have shrunk from the walls of 
the cells except the end walls. In a still older vessel the protoplasmic contents are 
greatly reduced and have passed into a dark-coloured mucilaginous mass at one or both 
ends of the cells near the transverse walls, whose dissolution takes place only very late in 
the development of the vessel, and may even be incomplete in the mature root. 
In no case was there any trace of the origin of vessels by the breaking down of more 
than one cell in the lateral direction as described by T. G. Hill for Dioscorea (21). 
The order of appearance of the vessels is centrifugal, the large scattered vessels when 
present being the first to appear in centrifugal order, followed in turn by the metaxylem 
and the protoxylem of the bundles, the last elements to develop being the external 
vessels of the protoxylem. "Thus the Palms conform to the account given by Buscalioni 
(22) and Pirotta (24) for several Monocotyledons, and confirmed by T. G. Hill (21) in 
Dioscorea. Lignification of the xylem takes place in a centripetal direction. 
Sieve-tubes. 
The sieve-tubes are principally grouped together into phloem-bundles alternating 
radially with the protoxylem group. In Latania Commersonii (Pl. 50. fig.72), however, 
they occur also in strands scattered throughout the fibrous zone among the large 
internal vessels. Phloem also occurs in a few roots in connection with the vessels in the 
medullary strands described below, and in Jriartia, as already mentioned, what appears 
to be an immature sieve-tube occupies the centre of each fibrous group in the cortex. 
The sieve-tubes are generally rather large thin-walled elements with somewhat oblique 
sieve-plates. Very little callus was found in any of the tubes. Ge 
The companion-cells are thin-walled elements with tapering extremities. 
Arrangement of Xylem and Phloem. 
Some roots conform to the typical monocotyledonous type in having all the vessels 
arranged in definite bundles, with exarch xylem followed internally by a series of 
gradually increasing metaxylem elements. This is found in Kentia Forsteriana (Pl. 50. 
fig. 75) and Sabal filamentosa (Pl. 50. fig. 74). i: 
More frequently, however, a series of internal vessels not referable to any partieular 
xylem-groups is also present. In Pheniz dactylifera (Pl. 50. fig. 68) only a few of these 
