26 i 
Dischidia rafflesiana ( Wall .). 
external surface, as the piliferous layer soon perishes. Later 
on again, an external periderm is formed, usually originating in 
the cells next below the exodermis. Subsequently peridermal 
arcs may be formed further towards the interior, by which 
groups of Sclerotic cells are often excised. In all the cases ob- 
served, however, the greater part of the cortex was persistent. 
The finer branches of the pitcher-root usually have a diarch 
or triarch cylinder. Where they are flattened against the 
sides of the pitcher their structure is somewhat dorsiventral, 
the cortex being decidedly thinner on the adherent than on 
the free side. The same peculiarity was also observed in the 
ordinary adventitious roots. 
The exodermis is remarkable for its very characteristic 
passage-cells (see Figs. 12 and 13), which are arranged with 
great regularity in longitudinal rows. The form of the cells, 
as seen in radial section, appears conical, the convex base of 
the cone bordering on the piliferous layer, while the somewhat 
truncated apex abuts on a protuberance of the cortical cell 
below. The side-walls are in contact with the other exo- 
dermal cells. 
The passage-cells have much denser protoplasm than the 
other exodermal cells. The cuticularization of the various 
cell-walls was tested, and it was found that all the walls of 
the exodermal cells are somewhat cuticularized, with the 
exception of the inner walls of the passage-cells. The outer 
walls of these cells are only partially cuticularized, the middle 
layers of the membrane giving cellulose reactions. The outer 
cell-walls of the piliferous layer, as well as those of the root- 
hairs themselves, are cuticularized 1 . It is evident that a thin 
layer of cuticle does not hinder absorption ; as however the 
walls of the passage-cells are certainly less cuticularized than 
those of their neighbours, we may assume that they really 
have a special conducting function to perform. 
The ordinary adventitious roots do not differ very strikingly, 
so far as we observed, from those in the pitchers. Their root- 
1 This is common in root-hairs. See Strasburger, Bot. Practicum, 2te Auflage, 
p. 280. 
