yr" 
MUCILAGE-CANALS OF THE MARATTIACER. 447 
condition, just as are those of the adjacent epithelium. The 
epithelium itself is so well marked and distinctly differentiated 
in the younger canals, that it is quite out of the question that 
it should be only an apparent epithelium resulting from the com- 
pression of the surrounding parenchyma by the mucilage, as was 
asserted to be the case by Kiihn for the Marattiaces generally, 
although his observations were only made on roots, and in only 
one species of each of the three genera which he examined. 
Fig. 8 represents a mature canal in a condition not infrequently 
found, even in old fronds, and it is difficult indeed to reconcile 
the appearance of its epithelium with Kiihn’s statement just 
referred to*. The cell br.c.’ was probably a bridge-cell in the 
young condition of the canal, and the appearance at bis probably 
due to an early tangential division in one of the initial cells. It 
is quite common to find adult canals in which it is difficult to recog- 
nize the epithelium at all, owing to its being compressed by the 
mucilage in the cavity, or perhaps owing to the epithelial cells 
being in a state of collapse after discharge of the mucilage, 
or secretion which ultimately become converted into mucilage. 
Careful examination, however, reveals that the epithelium is 
there, and it becomes at once evident on treatment with iodine, 
as its constituent cells contain numerous small grains which give 
the starch reaction. In longitudinal section the adult epithelial 
cells are seen to be considerably longer than broad (three to five 
times in UM. cicutefolia), with an evident nucleus and finely 
granular protoplasm. Their ends are sometimes square, some- 
times pointed. There is some evidence that they occasionally 
break down, owing to the pressure of the secretion, but such 
appearances are rare and were only observed in old canals. 
In the young developing canals of the frond of Angiopteris 
evecta, Marattia alata and WM. cicutefolia, 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 safranine or 
hematoxylin ; whereas in the adult condition the cavity is filled 
with a substance, “ mucilage,” which stains strongly with these 
reagents. It is possible, however, that a secretion might be 
present which is readily soluble in water, through which all 
the sections were passed before examination. The mucilage of the 
adult canals, however, is not at all readily soluble in water, only 
swelling therein. The true mucilage-canals found in the root of 
* In ‘Flora,’ 1889, p. 481. 
