THE ARCHEGONIAT^E 



211 



The Sporophyte 



As in Riccia, the first division in the fertilized egg is transverse; but only the 

 upper half of the em- 



A. 



bryo gives rise to 

 sporogenous tissue, 

 the proximal half de- 

 veloping into a short 

 stalk, or seta, whose 

 lower end forms a 

 foot, which is buried 

 in the tissue of the 

 gametophyte (Fig. 

 159). 



The upper part of 

 the sporophyte, the 

 capsule, has a definite 

 wall composed usually 

 of a single persistent 

 layer of cells, whose 

 walls may develop 

 thickenings upon 

 their inner surface. 

 The rest of the cap- 

 sule is composed of 

 the archesporium, 

 some of whose cells 

 develop into well- 

 marked elaters, the 

 others forming spores 

 in the usual way. 

 The dehiscence of the 

 capsule may be irreg- 

 ular, or there may be 

 a lid formed, which 

 falls away when the 

 spores are ripe. The 

 Marchantiacese com- 

 prise the most conspicuous of the Hepaticse, such genera as Marchantia, Cono- 

 cephalus, and Lunularia being among the best-known forms. 



V. 



FIG. 169. Marchantia polymorpha. A, plant with gemma- 

 cups, k (natural size). B-F, development of the gemma 

 (x 525). G, an older gemma, attached to its pedicel, and 

 showing the two growing-points, v, v' (x 260) . 



Order II. Jungermanniales 



The majority of the Hepaticae belong to the Jungermanniales, 

 which are especially abundant in the mountain forests of the Tropics. 

 Most of them are epiphytes, and may be found on the bark of trees in 

 every wood, although a few e.g. Blasia, Fossombronia occur upon 

 the ground. The gametophyte in the lower forms is a simple thallus, 

 but the greater number are leafy forms the so-called "Scale 

 Mosses." With very few exceptions, the gametophyte is markedly 

 dorsiventral in structure. 



