78 MOSSES AND FERNS chap. 



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. 30, 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 globular 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 

 level of the thallus, instead of penetrating into it, as is usually 

 the case. The stalk or portion between the capsule and foot 

 remains short, and in longitudinal section shows about four 

 rows of cells. As the calyptra grows the upper part becomes 

 divided into two layers, the part surrounding the foot into 

 three. Instead of breaking through the calyptra at maturity, 

 the capsule grows faster than the calyptra long before it is 

 mature, and the upper part of the calyptra is first compressed 

 very much and finally completely broken through by the 

 enlarging capsule, 



Leitgeb ^ calls attention to the fact that soon after the 

 cells of the archesporium begin to separate, the whole mass 

 of cells becomes completely separated from the wall of the 

 capsule, which grows rapidly until the cavity within is 

 much larger than the group of archesporial cells, which thus 

 float free in the large cavity.' Fig. 30, D shows a section 

 through a sporogonium at this stage. The cells making up 

 the central mass are apparently alike, but Leitgeb ^ says that 

 in the living sporogonium part of the cells have abundant 

 starch and chlorophyll, while in the others these are wanting 

 or present in much less quantity, while their place is taken by 



^ Leitgeb (7), vol. iv. p. 70. " Leitgeb, I.e. 



