17.] CHAPTER II. SPECIAL MORPHOLOGY OF THE MEMBERS. 



85 



ing cushion-like gametophores, or, more precisely, archegonio- 

 phores. When, as in most Ferns, the adult gametophyte is a flat- 

 tened dorsiventral cellular expansion, the archegonia are borne 

 on a cellular cushion projecting on the ventral surface, which 

 constitutes the archegoniophore. This kind of archegoniophore 

 reaches its highest development in the Fern Gymnogramme lepto- 

 phylla, where the cushion grows out into a tuberous subterra- 

 nean archegoniophore. 



When the shoot is differentiated into stem and leaf, the sexual 

 organs are in some cases borne on more or less specialised leaves 

 which may be termed 

 ytymetophylls, as in some 

 Algae, such as the Cha- 

 raceae (both antheridia 

 and oogonia), the higher 

 Sphacelariese (gametan- 

 gia of Cladostephus) and 

 the Rhodomeleae (e.g. 

 antheridia of Polysipho- 

 nia). 



The sexual organs may 

 either be scattered over 

 the surface of the mem- 

 ber bearing them, or they 

 may be developed in 

 groups (sori). Occasion- 

 ally a sorus is enclosed 

 in a receptacle ; such re- 

 ceptacles are the concep- 

 tacle of the Fucaceae and 

 of the Corallineae (Flori- 

 deae) ; the spermogonium of the Ascomycetous and ^Ecidiomycetous 

 Fungi ; the receptacle of many Hepaticae. 



In some Hepaticae (e.g. foliose Jungermanniese), and in all 

 Mosses, the sorus of sexual organs is surrounded by leaves, which 

 may differ more or less from the ordinary foliage leaves. The 

 investment thus formed is termed a perichcetium, and the leaves are 

 termed perichcetial leaves. 



Since, as has been pointed out, the gametangia correspond to 

 the sporangia, the gametophore corresponds also to the sporophore ; 

 they are both portions of the shoot, or of the thallus, which are 



Fig. 44. Himanfhal ia lorea (mu^h reduced), o 

 vegetative part of body ; b branched gametophore. 



