of the Anatomy of the Genus Selaginella , Spr. 151 
that they are only peculiarly modified cells of the inner general 
cortex, and not the specialized innermost layer of the cortex 
usually termed endodermis, then one would not so anxiously 
seek for the characteristic local thickenings on the radial walls. 
In any case my observations do not lead me to believe that 
the cuticularization is at all local in origin, but rather that it 
is an isolated product of the cuticle which uniformly covers 
the outer layer of the pericycle. As figured by Treub, the 
first stage in the development of a trabecula is the isolation 
(by a surrounding air space) of a cell stretching from the layer 
which will become the pericycle to the cortex. The pericycle 
has even at this stage a very thin cuticle. Subsequently the 
cuticle creeps up and invests the mother-cell of the trabecula, 
or rather the inner of the two cells into which the mother-cell 
has by this time divided. This inner cell is the future endo- 
dermal cell. The outer cell then divides by a radial division 
plane into two cells whose outer ends next the cortex remain 
narrow, but whose inner terminations swell considerably and 
form two balloon-shaped cells articulating with the endodermal 
cell (PL IX, Figs. 3 - 5 ). These then separate from each other 
at the cortical side and then through their entire length. 
Meanwhile differential growth causes elongation of the endo- 
dermal cell, so that the cuticularization becomes isolated as 
a ring. As has been pointed out by Strasburger (24), older 
endodermal cells may shew partial or complete cuticularization 
as a secondary phenomenon. This is what one would expect 
to take place when differential growth has ceased. Where the 
endodermal cell runs straight across the lacuna the annular 
band is median or nearly so, owing to equal growth in extent 
of the endodermal cell-wall between the annulus and the cortex 
on the one hand and the pericycle and annulus on the other. 
In the creeping axes of S. Lyallii , X. inaequalifolia and other 
forms where practically no lacuna is developed, and between 
the primary and accessory steles of many primarily tristelic 
species, the endodermal cells or their analogues are completely 
cuticularized, or at all events exhibits no cuticular annulus. 
I look upon this peculiar cuticularisation merely as a special 
