DEVELOPMENT OF THE SPOROGONIUM IN THE MOSSES. 273 
cortical tissue of the apophysis in Polytrichum differs from 
what is more usually found in possessing so few and such small 
intercellular spaces. In most other forms the development 
of intercellular passages is very large; and in Splachnum vas- 
culosum the cortical tissue of the apophysis is very similar to 
the trabecular tissue surrounding the spore-sac of the Musci 
generally. 
In the apophysis of Polytrichum formosum the central strand 
is reduced, and loses some of its distinctive characters. The 
cells become less elongated and more isodiametric in the upper 
parts of the apophysis, and the tissues are no longer distinguish- 
able into leptoxylem and leptophloém, as protoplasm is found in 
all the cells. 
In the more highly differentiated apophyses of P. piliferum 
and P. commune the central strand retains its characters, although 
they are gradually Jost in the stalk connecting the apophysis with 
the sporangium ; the leptoxylem is more largely developed than 
in the seta, and, as seen in transverse section, the leptophloém 
does not form quite so deep a zone round it nor are its limits 
distinctly defined (Pl. IX. fig. 9). 
The lower end of the sporogonium, which is inserted into the 
stem of the oophyte of the moss, is called the Foot. Its struc- 
ture is interesting on account of its physiological importance as 
theorgan by means of which the absorption of liquids takes place. 
All the water, with the substances in solution required for the 
nourishment aud transpiration of the sporogonium, must be 
taken up by the foot. From the size and complexity of the 
organs of the sporogonium and from the number of the stomata, 
it is obvious that these processes must be very active. 
The foot is from ] to 3 inch in length; it tapers downwards, 
and the tip is, as has been mentioned, turned up (Pl. IX. fig. 2). A 
careful examination of both transverse and longitudinal sections 
shows that the foot has pushed its way into the tissues of the 
stem of the oophyte. This is apparently effected by the cells of 
the young calyptra becoming hard and thick-walled before it 
is separated from the vaginula*. Consequently, when the young 
sporogonium grows in length, the calyptra for some time prevents 
it from pushing upwards its upward-growing apex, so that the 
* According to Hy (10) the cell-walls of the archegonium (future calyptra) 
are strongly thickened after the fertilization of the ovum (oosphere), 
