424 BOTANY PAIIT n 



anatomically of a simple structure ; if conducting strands are present, 

 they are composed merely of simple elongated cells. The sexual 

 organs are produced on the adult, sexual generation ; in the thalloid 

 forms, on the dorsal side of the thallus ; in the cormophytic forms, 

 at the apex of the stem or its branches (Fig. 378). 



By the division of the fertilised egg (Fig. 376 6'), a multicellular 

 embryo is formed, which, by its further development, gives rise to 

 the second or ASEXUAL GENERATION, represented by the SPOROGONIUM 

 or the stalked MOSS CAPSULE. The sporogonium, in most cases, 

 consists of a round or oval capsular receptacle, in whose internal 

 tissue numerous unicellular spores are produced. At maturity the 

 capsule opens and sets free the spores. In both the Bryophytes and 

 Pteridophytes the spores are formed in TETKADS by the twice-repeated 

 division of the spore-mother-cells, which previously have separated 

 from one another and become rounded off, and represent the actual 

 point of commencement of the sexual generation. The spore capsule 

 has usually a shorter or longer stalk, of which the basal portion, or 

 foot, remains in the distended venter of the archegonium, and, in 

 consequence of the overgrowth of the underlying tissue, has the 

 appearance of being sunk in it. Although the sporogonium constitutes 

 a distinct asexual generation, it continues throughout its existence 

 united with the sexual generation, and, like a semi-parasitic plant, 

 draws from it the nourishment necessary for its development. 



As shown by the occasional occurrence of intermediate structures, the antheridia 

 and archegonia are homologous organs ; the ventral-canal-cell and the iiffk-ranal- 

 cells of the latter represent gametes which have become funetionless f 94 ). Morpho- 

 logically the sexual organs of Archegoniatae are most closely comparable with the 

 plurilocular gametangia of the Phaeophyceae, while no close relation can lie tr;n-<-d 

 with the higher Green Algae. Further, in certain Brown Algae (Dictyotn] a regular 

 alternation of generations is already present ; in this case, however, thegametophyte 

 and sporophyte exhibit a similar organisation. The form of the thalloid gami-t<>- 

 phyte of the lower Liverworts shows the most marked correspondence with tin- 

 Brown Algae. The sporophyte of Bryophyta has proceeded on other lines <>f 

 development, but recalls the tetraspore formation in Dictyotn by the tetrad division 

 of the mother-cells of the asexual spores. 



The two very distinct classes of Bryophytes may be briefly charac- 

 terised as follows : 



1. Hepaticae (Liverworts). The sexual generation, with poorly 

 developed and generally not distinctly differentiated protonema, is 

 either a dichotomously divided thallus or is developed as a leafy, and, 

 with few exceptions dorsiventral shoot. In the majority of Hepaticae, 

 in addition to spores, the capsule produces also elaters, sterile cells 

 which, in their typical development, become greatly elongated and 

 provided with spiral thickenings (Fig. 382 F). They conduct 

 nourishment to the developing sporogenous cells, and at maturity, 

 after the opening of the capsule, serve to separate and scatter the 



