in Blechnum and Osmunda. 
43 
We may now confine ourselves to the consideration of 
the secretory hairs, dealing with the woolly hairs later on. 
The free walls of the mucilage-cells become markedly cuti- 
cularised but the transverse walls undergo a mucilaginous 
change. It soon becomes manifest that they also experience 
a great increase of thickness on either side, and reagents 
demonstrate that the thickening layers are of the nature 
of callus. Further, one can observe a phenomenon of great 
interest, for both the wall and the callus-layers on either ' 
side are perforated by a number of fine holes, which may 
be readily recognised even by direct observation and without 
the use of reagents (Figs. 36, 41, 43). A similar perforation 
of the transverse walls has already been described by Behrens 1 
as occurring in the secretory hairs of Ononis spinosa , but 
in this case there is no callus present. The structure pre- 
sented by Osmunda regalis is very like that of certain 
forms of callosed sieve-tubes, and in its mode of arrangement 
— the transverse wall and its two callus-plates — it even more 
strongly resembles that described by Schmitz 2 for so many 
of the Florideae. We think it hardly necessary to refer at 
any length to the importance of these perforations in estab- 
lishing a continuity of the protoplasm between the various 
adjacent filament-cells, since one of us 3 has already treated 
of the subject in some detail, but we would only wish to 
point out that its existence affords yet another proof of 
the porosity of the cell-wall, and of the very intimate con- 
nection which probably exists between all the constituent 
cells of living plant-tissues. The mucilaginous and callosed 
wall also serves a most important function in connection 
with the discharge of the secretion, for whereas the cuti- 
cularised walls are both resistent and impervious, the trans- 
verse membranes readily take up water, and, rapidly swelling 
on all sides, they finally cause the rupture and separation 
from one another of the secretory cells of which the adult 
1 Behrens in Ber. deutsch. bot. Gesellschaft, Bd. iv (1886), p. 402. 
2 Schmitz in Sitzber. Akad. Wiss. Berlin, 1883, P* 215. 
3 Gardiner in Arbeit, a. d. bot. Institut z. Wurzburg, Bd. iii. p. 52. 
