CHAPTER IV 



THE JUNGERMANNIACE^ 



A VERY large majority of the Hepaticae belong to the 

 Jungermanniaceae, which show a greater range of external 

 differentiation than is met with in the Marchantiacese, but less 

 variety in their tissues, the whole plant usually consisting of 

 almost uniform green parenchyma. In the lowest forms, e.g. 

 Aneiira and Metsgeria, the gametophyte is an extremely 

 simple thallus, in the former composed of almost perfectly 

 similar cells, in the latter showing a definite midrib. Starting 

 with these simplest types, there is a most interesting series of 

 transitional forms to the more specialised leafy ones, where, 

 however, the tissues retain their primitive simplicity. All of 

 the Jungermanniaceae grow from a definite apical cell, which 

 differs in form, however, in different genera, or even in different 

 species of the same genus. Root-hairs are usually present, 

 but always of the simple thin-walled type. 



The gametophyte, with the exception of the genera Haplo- 

 imtrium, Calobryuvi, and Riella, is distinctly dorsiventral, and 

 even when three rows of leaves are present, as in most of the 

 foliose forms, two of these are dorsal and lie in the same plane, 

 while the third is ventral. In the thallose forms, while the 

 bilaterality is strongly marked, there is not the difference 

 between the tissues of the dorsal and ventral parts which is so 

 marked in the Marchantiaceai. In the lowest forms the 

 gametophyte is a simple flat thallus fastened to the substratum 

 by simple root-hairs, and develops no special organs except 

 simple glandular hairs which arise on the ventral side near the 

 apex, and whose mucilaginous secretion serves to protect the 

 growing point. In Blasia and Fossoinbronia we have genera 



