78 MOSSES AND FERNS CHAP. 



iv., p. 68) states that two or even more may be surrounded 

 by a common envelope. When ripe, the venter of the arche- 

 gonium is somewhat enlarged, but not so much as in Riccia. 

 The egg-cell is very large, oval in form, and nearly fills the 

 cavity of the single-layered venter. 



The first wall in the embryo is transverse, and divides the 

 egg cell, which before division becomes decidedly elongated, 

 into two nearly equal cells. Ordinarily in each of these cells 

 similar transverse walls are formed before any vertical walls 

 appear, so that the embryo consists of a simple row of cells. 

 As in the Marchantiaceae the first wall separates the future 

 capsule from the stalk, and in this respect Sphccrocarpus 

 approaches the Marchantiales rather than the Jungermanni- 

 ales. Following the transverse walls there are formed in all 

 the upper cells nearly median vertical ones, which are inter- 

 sected by similar ones at right angles to them, so that in most 

 cases (although this is not absolutely constant) the upper half 

 of the young sporogonium at this stage (Fig. 32, A) consists 

 of two tiers, each consisting of four cells. The lower part of 

 the embryo is pointed, and the basal cell either undergoes no 

 further division or divides but once by a transverse wall, and 

 remains perfectly recognisable in the later stages (Fig. 32, B, 

 C). The other cells of the lower half divide much like those 

 of the upper half, but the divisions are somewhat less regular. 



There next arise in all the cells of the upper half periclinal 

 walls, which at once separate the wall of the capsule from the 

 archesporium. This wall in the later stages (Fig. 32, C, D) is 

 very definite, and remains but one cell thick up to the time the 

 sporogonium is mature. The further divisions in the capsule 

 are without any apparent order, and result in a perfectly glob- 

 ular body composed of an outer layer of cells enclosing the 

 archesporium, which consists of entirely similar cells with 

 rather small nuclei and dense contents. While these changes 

 are going on in the capsule, the lower part of the embryo loses 

 its originally pointed form, and the bottom swells out into a 

 bulb (the foot), which shows plainly at its base the original 

 basal cell of the young embryo. This bulb is characterised by 

 the size of the cells, which are also more transparent than those 

 of the other parts of the embryo. 



Owing to the development of the stalk of the archegonium, 

 after fertilisation the whole embryo remains raised above the 



