GROUP II. BRTOPHYTA : HEPATIC-E. 321 



nature : each group of archegonia is situated between the bases of two 

 adjacent lobes. The complete elongation of the stalk does not take place 

 until the archegonia are fully developed, or even until one of them has 

 been fertilised. 



It is only in a few of the higher Marchantieae that there is a highly de- 

 veloped antheridiophore. In Marchantia a definite terminal receptacle is 

 formed; it is discoid inform, and it is elevated on an erect stalk (see Fig. 

 198 A) : it is compound, having several growing-points, each of which 

 gives rise to antheridia in acropetal succession, and then ceases to grow ; 

 the stalk has two ventral furrows, showing that it consists of two 

 coherent branches. 



In Marchantia the venter of each archegonium becomes surrounded by 

 a sac-like membrane, developed from the stalk-cell of the archegonium, 

 which is termed the perigynium (Fig. 194). The development of the 

 perigynium begins when the archegonium is nearly mature. 



FIG. 1S>8. J 1'ortion of a plant of 3Iarchantia polymorp'ia (t), with atitheridiophores. 

 B Portion of a plant with a cupule containing gemmae; v v apices of the two branches. 

 (After Sachs.) C An archegoniophore with a doubly furrowed (r) stalk t, bearing a 

 terminal branched receptacle of which s is one of the rays ; h perichaetium ; fc sporogonia. 



The distribution of the sexual organs is various : the plants may be 

 monoecious or dioecious (Marchantia). 



The Structure of the Adult Shoot. The dorsal portion of the shoot consists 

 in all the Marchantiacese, of parenchymatous tissue, made up of cells con- 

 taining chloroplastids, which includes a number of air-chambers, giving 

 it an areolated appearance, whence it is termed the air-chamber-layer. 

 The chambers are formed by the unequal growth of the cells near the 

 growing-point, in consequence of which the surface presents alternating 

 elevations and depressions. In Marchantia the primary air-chambers be- 

 come completely closed in ; at the central meeting-point the growth of the 

 superficial cells take place vertically, leading to the formation of vertical 

 rows of cells which subsequently separate, leaving a canal between them. 

 This structure is distinguished as a compound pore. Compound pores of 

 M.B. Y 



