4 H 
West.—On the Structure and Development of 
at this stage the cell-wall is also undergoing mucilaginous degeneration and 
can be seen only with difficulty in thin microtomed sections. However, the 
cell-wall can still be identified as a very thin line extending across the clear 
space produced by the contraction of the cytoplasm. It is worthy of note 
that Brebner (1. c., p. 447) observes that ‘ in the young developing canals of 
the frond of Angiopteris eve eta, Marattia alata , and Marattia cicutaefolia , 
there is little or no sign of mucilage, for there does not seem to be anything 
more highly refractive than the mounting medium in the schizogenous 
space, nor anything which stains appreciably with safranin or haema- 
toxylin, whereas in the adult con¬ 
dition the cavity is filled with 
a substance, “ mucilage ”, which 
stains strongly with these re¬ 
agents 
Charles (1. c., p. 96) also 
states that ‘ the space left when 
the walls break apart appears 
empty at first, then becomes filled 
with a vacuolate substance that 
stains with aniline blue \ 
The mucilaginous degenera¬ 
tion of the cell-wall proceeds 
apace until the cell finally col¬ 
lapses owing to the complete 
solution of the cell-wall. 
In this way, then, the cavity 
of the duct originates (Text-figs. 4 
and 6 ; Figs. 6 , 8, and 12-14). 
The rate at which individual 
cells become disorganized is very 
unequal; thus, several cells which appear quite healthy may be observed 
bordering on the duct at a comparatively early stage in its development 
(Text-fig. 6 ; Fig. 13, and cf. the ‘bridge-cells ’ of Brebner, 2 , p. 446). 
Sooner or later, however, they all share the same fate, their disorganized 
remains contributing to the mucilaginous contents of the duct, which is now 
surrounded by the unmodified cells of the ground tissue (Text-fig. 7; 
Figs. 7 and 9, m.c.). 
Treatment with iodine, as recommended by Brebner (2, p. 447), failed 
to reveal the presence of an epithelial layer. 
The important factor of tissue-tensions, which has been admirably 
elucidated by G. Kraus ( 12 ) and Newcombe ( 16 ), appears to have been 
completely neglected by all previous workers on the development of 
mucilage-ducts. 
Text-fig. 7. Transverse section of an adult 
mucilage-canal from the petiole of Archangiopteris 
Henryi , Chr. et Gies. Note complete absence of 
epithelial cells, x 380. m. = mucilage. 
