DEVELOPMENT OF PLANTS 257 



spore reproduction. But especially has this change been brought 

 about by the fact that the gametospore in germinating develops 

 an asexual plant or generation with enormous possibilities in the 

 way of spore production, so that the increase and distribution of 

 individuals is now fully provided for by the asexual plant and 

 consequently largely removed from the sexual plant. This shift- 

 ing of the responsibility for the increase in number of indi- 

 viduals from the sexual to the asexual generation is one of the 

 most significant departures in the evolution of plants. We will 

 be interested to note how this change came about and how it 

 steadily gains in importance in the remaining divisions. 



The sexual reproduction of the bryophytes reveals a series of 

 variations that are only remotely suggestive of the algae, but that 

 indicate very clearly relationship with higher plants. These 

 features will be considered in the discussion of the various groups. 

 There are two classes of Bryophyta: A, The Hepaticae or Liver- 

 worts; B, the Musci or Mosses. 



Class A. Hepaticae or Liverworts 



103. Classification of the Liverworts. — While these plants are 

 the simplest and least conspicuous of the Bryophyta, they are the 

 most interesting, because among them will be found reminders of 

 the algae and at the same time they present many features that 

 are suggestive of the mosses and ferns. They occur in very 

 moist places and in deep woods, on rotting logs and moist shady 

 banks. A few are aquatic, floating upon still ponds and streams, 

 and some have become adapted to dry conditions. There are 

 three orders: (a) Marchantiales or Thallose Liverworts; (b) 

 Jungermaniales or Leafy Liverworts; (c) Anthocerotales or 

 Horned Liverworts. 



104. Order a. Marchantiales or Thallose Hepatics. — The 

 liverworts of this order are characterized by flat, prostrate and 

 rather fleshy bodies which usually grow upon the earth, to which 

 they are attached by numerous rhizoids. Owing to the frequent 

 division of the apical cell of the thallus into two equal parts, there 

 result two growing points which thus produce the equal forking 

 or dichotomous branching of the thallus, so characteristic of these 



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