CHAPTER XXVI 

 BRYOPHYTES 



This group ol plants consists^ of the liverworts (Hepaticce) 

 and mosses (Miosci). They are of very little econO'inic import- 

 ance, but it is very necessary to have a thorough knowledge of 

 them in order to understand the evolution of the higher plants. 

 The evolutionary evidence indicates that they were derived from 

 the algae and that they were the first land plants in. the history of 

 the plant kingdom. A high moisture; content is necessary for 

 the growth of most of the mosses ; in fact, some species live in 

 the water. Their life history involves what is known as the 

 Alternation of Generations; i.e., a life history consisting of two 

 types of plants alternately producing each other; one generation 

 known as the gam.etoph'ifte producing sexual organs bearing the 

 gametes or sex cells, and one generation known as the sporophyte 

 producing non-sexual spores. 



The archegonium or female sex organ is characteristic of 

 both the Bryophytes and the Pteridophytes. In fact, these two 

 great groupsi are sometimes referred to as the archegoniates. The 

 appearance of the highly developed, multicellular antheridium or 

 male sex organ is also very characteristic of the Bryophytes. 



The Hepaticce is a v^ry old groxip of plants which were 

 probably of much greater importance in some earlier period of 

 the history of the plant kingdom than at present. It is divided 

 into three divisions: (1) Marchantiales, (2) Jungermanniales 

 and (3) J nthocerotales. One of the most common and most 

 conspicuous species in Marchantia polymorpha (Figs. 13Y, 138, 

 139, 140, 141), which is a most excellent type of study. 



The gametophyte of Marchantia polymorpha is a highly de- 

 veloped thallus (Fig. 137), much larger than in most of the 

 Hepafica'. It is ilat, branching and several layers of cells in 

 thickness. It is much thicker in the axial line than on the mai^ 

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