VASCULAR CRYPTOGAMS. 
end is directed backwards, its inner deeper end facing the anterior margin. At this 
latter point lies at a subsequent period the apical cell of the embryonal stem. Young 
archegonia have the apex of their central cell covered with four superficial cells 
arranged in the form of a cross ; in each of these latter a wall arises inclined from 
without inwards and downwards, followed in each inner cell by another similar 
partition (Fig. 3 1 2 /, <2, 3, c). By the succeeding growth these cells are transformed 
into four rows, each consisting of three segments lying one above another, forming 
the neck (//, ///), the lower of which are termed 'closing cells,' the upper pair 
the 'stigmatic cells' (///, h). In the meantime a new cell arises at the apex of 
the central cell, which, with its conical point, forces itself between the closing 
cells (/, d, HI, d), and forms the canal-cell, first discovered by Pringsheim; ac- 
cording to Janczewski a small segment is cut off from the upper part of the 
central cell to form the ventral canal-cell, so that here, as in the other Vascular 
Cryptogams, two canal-cells are developed. The two canal-cells become transformed 
Fig. 314— Marsüza Salvatrix; A pt the prothallium projecting through the ruptured membrane r of the spore ; si the 
mucilaginous epispore which forms the funnel, with a number of antherozoids ; B vertical section of a prothallium pt with 
an archegonium a and oosphere o ; C, D, E young embryos, j apex of the stem, b leaf, w root,/" foot (B—E after Hanstein). 
into mucilage, which escapes from the canal laid open by the throwing off of the 
stigmatic cells. The large remainder of the central cell (/, //, ///, e) becomes 
the oosphere. After fertihsation has been accomplished, the canal again closes 
by the lateral approximation of the ' closing cells.' 
The prothallium of MarsiUa and Pilularia projects as a hemispherical mass of 
tissue from the apical papilla of the macrospore, after it has ruptured the walls 
of the spore at that place (Fig. 314, A, B), and remains buried at the bottom 
of the funnel formed by the epispore of the macrospore. Even at an early period, 
before the rupture, Hanstein asserts that the large central cell may be recognised in 
it, surrounded, in its entire circumference, at least at first, by a single layer of cells, 
so that the prothallium bears originally only a single archegonium. The central 
cell is here also covered by four cells arranged crosswise, which form at the same 
time the apex of the whole prothallium. By a similar process to that which occurs 
