THE BRYOPHYTA : HEPATICAE, THE LIVERWORTS 389 



develops a theca or capsule containing asexual spores. In the production 

 of these spores meiosis occurs and the monoploid condition is re-established. 

 In the Bryophyta this sporophyte never becomes independent, but remains 

 attached to the gametophyte throughout its life, although by producing 

 chloroplasts, as it does in Mosses, it provides to some extent its own food. 

 In general terms, we may say that the gametophyte, which is the principal 

 phase of the Br}'ophyte plant, produces a sporophyte which lives parasiticallv 

 upon it. This sporophyte of the Bryophyta is called the sporogonium and 

 it produces the capsule in which the spores develop. 



The type of alternation of generations found in the Bryophyta, where 

 the two generations are different morphologically, is spoken of as 

 heterologous, whereas the type seen in Dictyota, where both generations 

 are structurally identical, is called homologous. 



As we pass from the Br^'ophyta through the subsequent phyla we shall 

 find a gradual reduction in the importance of the gametophyte and a corre- 

 sponding increase in the complexity of the sporophyte, until in the Flowering 

 Plants the whole plant is a sporophyte and the gametophyte is reduced to a 

 minute structure enclosed within it. 



The Bryophyta comprise the Mosses and the Liverworts and are divided 

 botanically into two classes : — 



1. Hepaticae, the Liverw^orts. 



2. Musci, the Mosses. 



HEPATICAE 



The Hepaticae are Bryophyta in which the plant is alwavs dorsiventral 

 and is frequently prostrate and thalloid, while the spores are developed in 

 relatively simple sporogonia without chlorophyll, except in the Antho- 

 cerotales. In the simpler members the thallus is flat, prostrate and 

 dichotomously branched, and secured to the ground by simple processes 

 called rhizoids. Some of the niore advanced members develop an axis on 

 which leaves are produced. They are included in the order Jungermanniales, 

 as the Foliose Liverworts. 



The members of the Hepaticae grow chiefly in damp, shadv situations, 

 by the edge of streams, on marshy ground and a few in the water. \'ery few- 

 can withstand serious desiccation and they do not like drv habitats. 



The sex organs consist of antheridia and archegonia and may be produced 

 on the same or on different plants. The sporogonium, as we have seen, 

 develops from the archegonium as a result of fertilization and lives for a 

 time as a parasite. In it the spores are developed, from which fresh plants 

 are produced. Some species develop detachable vegetative organs termed 

 gemmae, small multicellular bodies which after liberation can develop into 

 fresh plants. 



The Liverworts are geologically an ancient group, fossil remains of 

 which are known from as far back as the Coal Measures. 



