432 DR. ERIC DRABBLE ON THE 
A transverse section through the apex in the region of the meristem-group shows 
radiating lines of cells extending from the centre to the periphery, the various layers of 
the root arising by subsequent differentiation in these cells. 
Root-cap. 
A longitudinal section of the apex shows the root-cap to be merely a local 
specialization of parenchyma formed from the extremities of the rows of cells radiating 
from the common meristematic group. As these cells approach the surface they become 
elongated (Pl. 48. fig. 13) and gradually exfoliate. The cells are dark-coloured; the 
middle lamella is destroyed by strong sulphuric acid, and the individual elements can 
be thus isolated. The internal walls are highly cuticularized and very resistant to the 
action of the acid. 
In the outer cells the lumina may be entirely occluded by a dark-coloured substance 
giving cork-reactions. 
Partial occlusion resulting in considerable reduction of the lumen may occur in more 
internal cells of the root-cap (Pl. 48. fig. 14). 
The macroscopic appearance presented by the root-cap in Kentia and most other forms 
is that of a much-indurated dark-coloured smooth coating to the apex, extending for 
about an inch up the root (Pl. 48. fig. 11). 
In Areca sp. (Pl. 48. fig. 12) and Zriartia sp. a different form of root-cap is shown. 
Instead of presenting a smooth surface, the outer layers of the cap are partially exfoliated 
and appear as an irregular covering of overlapping scales, closely resembling the same 
structure in Philodendron figured by Olivier (8) and in Pandanus figured by Van 
Tieghem (16). 
The Limiting or Piliferous Layer. 
An inch or so from the apex the root-cap is entirely exfoliated, or only represented 
by a few isolated broken-down elements adhering to the surface of the root. More 
proximally the surface is occupied by the so-called “limiting layer" (‘epidermis ” 
of authors) The term “ piliferous layer" is not generally applicable in a strict sense 
in Palms, as in no case was any development of root-hairs observed. Gillain (12), 
however, appears to have found them in one instance, as he says: “nur bei Trachycarpus 
excelsus, finden wir Haargebilde.” The cells of this layer frequently project as 
papilliform structures, as described and figured by Karsten (2) for Iriartia. 
The walls of this layer are generally cuticularized and comparatively thin. This layer 
is shown for Kentia in Pl. 48. fig. 14; for Caryota ochlandra in Pl. 48. fig. 15; for 
Phenix sylvestris in Pl. 48. fig. 16; and for Dypsis madagascarensis in Pl. 48. fig. 17. 
The limiting layer does not represent any definite morphological stratum, but cuts 
through a series of lines of cells radiating from the meristem. It can be traced in an 
apical direction for a considerable distance underneath the root-cap, the cells becoming 
gradually smaller the nearer they approach to the apex. At the apex itis quite impossible 
to say which cells will form the limiting layer. 
Ke The cells of this layer do not necessarily form a perfectly regular sheath, irregularities 
such as that figured in fig. 14 being not uncommon. 
