384 



BOTANY 



developed, but in their stead rhizoids, consisting of colourless branching 

 filaments. The Bryophytes, in this respect, differ essentially from the 

 Pteridophytes, which are provided with true roots. The stems and 

 leaves of Mosses are also anatomically of a simple structure ; if con- 

 ducting 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. 313). 



By the division of the fertilised egg, 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 cap- 

 sular receptacle, in whose internal tissue 

 numerous unicellular spores are pro- 

 duced. At maturity the capsule opens 

 and sets free the spores. In both the 

 Bryophytes and Pteridophytes the 

 spores are formed in tetrads by the 

 twice-repeated division of the spore- 

 mother- cell, which previously become 

 disunited, representing the actual point 

 Fia.si3.-Pho5cum cuspidatnm. another- of commencement of the sexual genera- 



idia ; ar, archegonia at the apex of the tion. The spore Capsule has Usually a 

 bifurcated moss stem; i, leaves ;p para- shorter or ] onger stalk f which tne 

 physes. (After Hofmeisteb, x45.) a ' ... 



basal portion, or toot, 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 draws from it the nourishment necessary for 

 its development. 



The two classes comprising the Bryophytes may be briefly charac- 

 terised as follows : — 



1. Bepaticae (Liverworts). — The sexual generation, with poorly developed and 

 generally not distinctly differentiated protonema, has either a diohotomously divided 

 thallus or is developed as a leafy, and, with one exception, 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 pro- 

 vided with spiral thickenings (Fig. 317, F). They conduct nourishment to the de- 

 veloping sporogenous cells, and at maturity, after the opening of the capsule, serve 

 to separate and scatter the spores. Only in one order, Anthocerotaceae, does the 

 capsule have a columella, or an axial mass of sterile cells, which also conduct the 

 metabolic products to the developing spores. 



