332 PART III. THE CLASSIFICATION OF PLANTS. 



sporiura being ruptured, the contents, covered by the endosporium, 

 then generally grow out in the form of a filament, which is the 

 beginning of the protonema. In some rare cases (e.g. Pellia, 

 Andreaea) cell-divisions take place within the spore before the 

 exosporium is ruptured, so that the protonema is from the first a 

 mass or a layer of cells. 



The body developed from the oospore, which constitutes the 

 asexual generation or sporophyte of the Bryophyta, is termed the 

 sporogonium. With regard to its general morphology it may be 

 considered (except in Riccieae) to present differentiation into root 

 and shoot ; the foot, however rudimentary, developed from the 

 hypobasal half of the oospore, represents the root ; the capsule and 

 the seta (when present), developed from the epibasal half of the 

 oospore, represent the shoot. The shoot is in no case differenti- 

 ated into stem and leaf. .In the Riccieae the products of the 

 hypobasal and epibasal cells are quite similar, so that the whole 

 thalloid sporogonium consists only of a capsule. Hence, whilst it 

 is the rule in the Bryophyta that sporogenous cells are only de- 

 veloped in the shoot-portion of the sporophyte, that is, are derived 

 only from the epibasal cell, in the Ricciese the derivatives of the 

 hypobasal cells are also sporogenous. 



The sporogonium is not an independent sporophyte, but remains 

 attached to the gametophyte, obtaining from it either the whole 

 or a portion of its food. It must, however, be clearly understood 

 that there is no continuity of tissue between the two germinations ; 

 the sporophyte is simply inserted into the tissue of the gameto- 

 phyte. In the Hepaticae the sporophyte is short-lived (except in 

 Anthoceros), and is entirely dependent upon the gametophyte for 

 its nutrition. In Anthoceros, and in most of the Musci, the capsule 

 possesses more or less well-developed assimilatory tissue, and its 

 epidermis is provided with stomata, so that the sporophyte is 

 capable of using the carbon dioxide of the air as its carbonaceous 

 food, and is dependent upon the gametophyte only for its supply 

 of water and salts. In many of these forms the seta has a central 

 strand of rudimentary vascular tissue through which the water 

 and salts, absorbed from the gametophyte, can travel to the region 

 of the capsule where assimilation and transpiration are carried on. 



The Bryophyta (Muscineae) are divided into two classes, the 

 distinctive characters of which are as follows : 



Class III. HEPATICJE (Liverworts). 



Gametophytic Characters. Protonema, generally short-lived, in- 

 conspicuous, a flattened expansion. 



