Ml 'SCI AND HEPATICAE 



47 1 



of the wall, parts of which are photosynthetic while young. Thus far the 

 sporogonium is enclosed in the growing venter of the archegonium (Fig. y>6). 



As it develops further the lower part remains thin, 

 forming the seta, which may be traversed by a 

 conducting strand (Fig. 364). But the distal part 

 enlarges to form the capsule. A layer of cells is 

 there cut off from the periphery of the endothecium, 

 and acquires dense contents. This is the arche- 

 sporium, which is shaped like a barrel without 

 ends {arch. Fig. 364). Within it is the large-celled 

 water-storage tissue of the columella. The amphi- 

 thecium, limited now by a superficial epidermis with 

 stomata, forms a lacunar photo-synthetic tissue, 

 with a large and continuous air-space outside the 

 archesporium. This tissue is specially active in that 

 region called the apophysis, where the stomata are 

 most frequent (st., Fig. 364). In some Mosses it 

 is enlarged as a very effective organ of nutrition. 



As the development proceeds the cells of the 

 archesporium divide repeatedly, forming a thick 

 cylinder of sporogenous cells surrounding the 

 columella, and limited externally by a double 

 layer of cells of the amphithecium. This con- 

 stitutes the spore-sac. Its cells then separate, 

 and rounding off in a liquid that fills the sac, each 

 undergoes tetrad-division, and finally produces four 

 spores. Reduction takes place as usual, common 

 numbers of chromosomes for Mosses being 12-6. 

 The numbers are low for Bryophytes generally. 

 The mature spore is very minute, and almost 

 spherical, and it contains globules of oil. 



Meanwhile above the fertile region certain inner 

 cells of the amphithecium undergo changes of induration of the cell-walls to 

 form the peristome, which is closely related to the liberation of the spores 

 {p., Fig. 364). As its structure differs in 

 detail in various Mosses, it provides facts 

 valuable in their classification. The case of 

 Fontinalis serves as a good example of a com- 

 plicated peristome, as it is seen after the oper- 

 culum falls away. It is double (Fig. 367). The 

 inner peristome forms a sort of connected lattice- 

 work which will allow the spores to pass singly 

 through its pores, but prevents them all falling out 

 at once. The outer consists of 16 teeth, which arc 

 really strips of thickened cell-wall, separated from 

 one another by the breaking down of the thinner 

 lateral connections. They show movements with 



Fig. 366. 



Young sporogonium of Physco- 

 mitrella patens, shown in outline, 

 shortly before the rupture of the 

 archegonial wall. (After Hy.) 



Fig. 367. 

 Fontimdis, apex of capsule (K) 



changes of moisture in the air, and catching one a f te r shedding the operculum 

 . . . - ., /i- 1 _.•__ a/> = outer peristome. «j£> = 



on another by their rough edges, they give flicking a p p cri ™™l 

 jerks on release, which throw the spores to a ( x 50.) 



(After Schimper.) 



