430 DR. ERIC DRABBLE ON THE 
ANATOMY AND HISTOLOGY OF THE Roots OF PALMS. 
Origin of Adventitious Roots in the Stem. 
The adventitious roots of the Palms have their origin in the pericyclic tissue of the base 
of the stem, in accordance with the method described by Van Tieghem and Douliot (13) 
for flowering-plants in general. The base of the stem is clothed with a dense cortex, 
usually very fibrous in nature and of considerable thickness, varying in different plants, 
but frequently several inches thick. Hence the pericyclic root arises deeply in the 
tissues of the parent stem. The root originates as a small papilla produced by division 
of the pericyclic cells. This papilla is provided externally with an extra-calyptral 
mantle or poche of small parenchymatous thin-walled cells, which presents its maximum 
thickness immediately over the apex of the papilla, thinning out laterally and exposing 
. the underlying cells of the root-papilla. 
Below the poche the apex is occupied by a group of meristematic cells, which, followed 
laterally, is seen to be separated into a thin external layer and a central group in which 
arises the procambial tissue, a zone of dark-coloured cells which eventually gives rise to 
the tegumentary system intervening between the two (Pl. 48. fig. 1, a, and fig. 3, a), exactly 
as figured by Karsten (2). The procambial tissue is here found in the form of a series of 
separate strands, which can be followed inwards into the stem for a considerable distance, 
running roughly at right angles to the stem-bundles (fig. 1, proc.st.). Thus only the 
distal extremities of the procambial strands are laid down in the shallow root-papilla, 
the internal portions arising by secondary divisions in the ground-tissue of the stem, 
as described by Mangin (9). The elements in this region are well differentiated, while 
the root itself is a mere pericyclic papilla (Pl. 48. fig. 1). 
A slightly older root (fig. 3) presents essentially the same features, The papilla is 
now, however, considerably elongated and flexed downwards. Over the apex is the 
poche, which is continued for only a short distance up the root, the tegumentary tissue 
being exposed above it. The procambial tissue is here also in the form of separate 
strands (fig. 3, proc.st.). 
In the cortex occur cells containing raphides. A transverse section through the apex ` 
of a pericyclic root-papilla shows a series of procambial groups of varying tangential 
extent scattered throughout the ground-parenchyma (fig. 7). In many cases the 
scattered procambial groups are much smaller and more numerous than in the root of 
Kentia figured. The more peripherally placed strands are delineated very definitely 
from the ground-parenchyma externally, but internally are much less distinctly 
bounded. 
Passage of the Root through the Oortex of the Stem. 
The root from its very inception projects into a well-formed cavity lying between it 
wé the surrounding cortical tissues (Pl. 48. figs. 1, 2, and 3,¢). This cavity is bounded 
. by ragged cells, which show very clear signs of solution and disintegration. The 
er external cells of the poche also show a similar appearance, and in some cases imme- 
S diately outside the poche quite a mass of disorganized tissue occurs. The fibres of the 
e 1 cortex resist. the solvent action longer than does the parenchyma, but eventually they, 
