CHAPTER III 

 THE JUNGERMANNIALES 



A VERY large majority of the Hepaticse belong to the 

 Jungermanniales, which show a greater range of external dif- 

 ferentiation than is met with in the Marchantiaceae, but less 

 variety in their tissues, the whole plant usually consisting of 

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

 Aneura 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 transi- 

 tional forms to the more specialised leafy ones, where, however, 

 the tissues retain their primitive simplicty. All of the Junger- 

 manniales grow from a definite apical cell, which differs in 

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

 of the same genus. Rhizoids are usually present, but always 

 of the simple thin-walled type. 



The gametophyte, with the exception of the genera Haplo- 

 mitrium, and Calobryum, 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 Marchantiales. In the lowest forms the gametophyte is a 

 simple flat thallus fastened to the substratum by simple rhizoids, 

 and develops no special organs except simple glandular hairs 

 which arise on the ventral side near the apex, and whose muci- 

 laginous secretion serves to protect the growing point. In 

 Blasia and Fossombronia we have genera that while still retain- 

 ing the flattened thalloid character, yet show the first formation 



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