44^ 



VASCULAR CRYPTOGAMS. 



end is directed backwards, its inner deeper end facin^^ 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 vv.iU arises inclined from 

 without inwards and downwards, followed in each inner cell by another similar 

 partition (Fig. ^12 I, a, b, 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. 3i4.—Af(irst'h'a Salvatrix; A ft\i\\e. prothallium projecting through the ruptured membrane r of the spore; j/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, s apex of the stem, b leaf, iv 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 fertilisation has been accomplished, the canal again closes 

 by the lateral approximation of the ' closing cells.' 



The prothallium of Marsilia 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 



