MUCILAGE-CANALS OF THE MARATTIACER. 445 
of the four genera which were examined was so suggestive of 
their being schizogenous intercellular spaces with a secretory 
epithelium, that a re-investigation was deemed advisable. The 
material available was an entire young plant of Angiopteris 
evecta (var. hypoleuca?) besides large aerial and other roots of 
the type form, roots of A. evecta var. pruinosa, roots of Marattia 
attenuata, a young pinnule of M. cicutefolia, and an entire young 
frond of MV. alata. All but the last-named—which was kindly 
supplied by Prof. F. W. Oliver—were from the Royal Gardens, 
Kew. 
The mode of origin of the mucilage-canals was found to be 
typically schizogenous except in the case of the roots of A. evecta 
var. pruinosa, which presented such peculiar features as to 
require special consideration after the more common mode of 
development has been dealt with. 
The most successful preparations of very early stages were 
obtained from the petiole of a very young frond of A. evecta. 
This frond was about 4 mm. in diameter at the base and 2 mm. 
in the region from which figures 1 to 6 inclusive were obtained. 
The vascular bundles were already well differentiated as distinct 
groups, and in the larger ones the walls of the protoxylem 
elements were already thickened, but that was all. In these 
sections certain cells of the ground-parenchyma are seen to have 
become meristematic, giving rise to little specialized groups of 
cells (Pl. XXXVII. figs. 1, 2, 3a). The constituent members 
of each group are smaller than the surrounding cells of the 
ground-tissue, the difference becoming more marked as the 
respective elements approach their adult condition. The four 
specialized cells in fig. 1 a, representing a very early stage of 
development, are not so markedly smaller than the surround- 
ing cells, firstly because the ground parenchyma is still very 
young, and secondly because the cells of the meristematic group 
divide again without subsequently increasing much in size. In 
Angiopteris the meristematic group is composed of from four 
to ten or more elements; this is due to the fact that what may 
be called the canal initials are not constantly formed by the 
meristematic division of one cell only. In these, moreover, the 
divisions are by no means always radial to the centre of the 
future canal, and it is owing to that fact that the mature epithe- 
lium is not infrequently locally more than one cell thick. The 
canal initials are readily recognized at a very early period in 
