274 MR. J. R. VAIZEY ON THE ANATOMY AND 
lower apex is forced down into the stem of the oophyte through 
the softer to the harder tissues, when the pressure on the 
calyptra becomes so great that it is torn away from the vaginula. 
By the foot being forced down in this way into the centre of the 
conducting tissues of the oophyte, a supply of food-material is 
assured to the foct. Transverse sections of the foot, with the 
surrounding tissue of the oophyte, show that the cells of the 
tissues of both structures, especially in the regions where they are 
in contact with one another, are gorged with protoplasm, and 
have large well-defined nuclei and nucleoli. Longitudinal sec- 
tions of material carefully prepared by hardening in absolute 
alcohol or 1-per-cent. chromic acid, and afterwards treated with 
alcohol, show the protoplasm of the cells in a highly granular 
condition with a striated, almost stringy or ropy, appearance, 
giving the impression that active circulation or rotation of the 
protoplasm was going on in the tissue while in a living condi- 
tion. The striations are usually slightly diagonal, but nearly 
parallel to the long axis of the seta. Transverse sections show 
that the foot has essentially the same structure as the seta, and, 
near its point of junction with the seta, is identical. A series of 
sections shows that, passing downwards, the leptophloém gra- 
dually diminishes, and that the leptoxylem, which, as in the seta, 
is totally devoid of protoplasm, increases. 
The cell-walls of the tissues of the foot are totally without 
colouring-matter—even the cortical sterome, which also is less 
sclerotic. The cortical parenchyma-cells are almost cubical in 
form, and are thicker-walled than in the seta. 
_ A median longitudinal section of the foot (Pl. X. fig. 15, Pl. 
XI. fig. 31) shows the change that takes place in the tissues of 
the centralstrand; the leptophloém is gradually reduced, so that 
at a short distance from the apex, instead of forming, in Poly- 
trichum, a zone five or six cells deep, it is reduced to two, the 
innermost cells of this layer, apparently taking on the functions 
and form of the leptoxylem, losing their protoplasmie contents. 
This process goes on til the whole of the central strand is 
transformed into a thin-walled prosenchyma without protoplasm 
(fig. 31). The cortical tissues of the apex undergo a similar 
change, and the intercellular spaces are lost a little above the 
apex. The epidermis retains its protoplasm. The apex of the 
foot consists solely of this thin-walled peer and some 
disorganized cells (tig. 31). 
