CHAP. Ill MARCHANTIE^ 67 



MarcJiantia ^ and other genera, a distinct two-sided apical cell 

 is usually developed at an early period, and for a time the 

 growth of the young plant is due to the segmentation of this 

 single cell. Finally this is replaced by a single four-sided cell 

 (Fig. 27, C), very much like the initial cell of the mature 

 thallus. The young plant, composed at first of homogeneous 

 chlorophyll - bearing cells, grows rapidly and develops the 

 characteristic tissues of the older thallus. The first rhizoids 

 are always of the simple form, and the papillate ones only 

 arise later, as do the ventral scales. Targionia shows a number 

 of peculiarities, being much less uniform in its development 

 than Fhnhriaria. While it often forms the characteristic 

 germ tube, and the divisions there are the same as in Riccia and 

 Fzmbriaria, the formation of a germ tube may be completely 

 suppressed, and the first result of germination is often a cell 

 mass, from which later a secondary germ tube may be formed 

 with the young plant at the apex (Fig. 26). Such cases as 

 these are the only ones where it seems really proper to speak of 

 the plant arising secondarily from a protonema, for in other 

 cases, as in Riccia, the growth is perfectly continuous, and the 

 axis of the young thallus is coincident with that of the germ 

 tube, and in no cases observed by me could it in any sense be 

 looked upon as a secondary lateral growth. 



Classification of the MarcJiantiecs 



The higher Marchantiese are readily separable into three 

 families, the Corsinieas, Targionieae, and the true Marchantiea;. 

 Leitgeb has made a further division of the latter family, but 

 some of the characters given are not sufficiently constant to 

 warrant his division, and for that reason it has been thought 

 best not to accept them.^ Thus Fimbriaria Californica, which 

 is, in regard to its fructification, typical, has the female recep- 

 tacle of the composite type, a character which, according to 

 Leitgeb, not only does not belong to the genus Fimbriaria, but 

 is not found in any genus of the group (Operculatae) to which 

 he assigns it. This species too does not have the capsule 

 operculate, but opens irregularly. The Corsinieae, as we have 



1 Leitgeb (7), vol. vi. PI. IX. Fig. 13. 

 - Leitgeb (7) and Schiffner (i), p. 24. 



