II MUSCINEX— HEPATIC^— MARCHANTIALES 67 



Riccia trichocarpa, but resemble them very closely in the com- 

 moner forms. 



In Fimbriaria especially, and this has also been observed 

 in Marchantia (Leitgeb (7), vi., PI. ix., Fig. 13) and other gen- 

 era, 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. 29, C), very much like the 

 initial cell of the mature thallus. The young plant, composed 

 at first of homogeneous chlorophyll-bearing cells, gro\Vs 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. Tar- 

 gionia shows a number of pe- 

 culiarities, being much less 

 uniform in its development 

 than Fimbriaria. While it 

 often forms the characteristic 

 germ tube, and the divisions 

 there are the same as in Riccia 

 and Fimbriaria, the formation 

 of a germ tube may be com- 

 pletely suppressed, and the 



Fig. 2S.—Targwnia hypophylla. Germ flj-g^- rcSult of germination is 

 plant in which the thallus (T) has . ° . 



been formed secondarily, X260. Olten 3. CClI maSS, frOm whlch 



later a secondary germ tube 

 may be formed with the young plant at the apex (Fig. 28). 

 Such cases as these are the only ones where it seems really 

 proper to speak of the plant arising secondarily from a proto- 

 nema, 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. 



Biology of the Marchantiaceae 



While the Marchantiaceae are, as a rule, moisture-loving 

 plants, still some of them are markedly xerophilous. Most of 

 the commoner Californian species, e.g., Fimbriaria Calif ornica. 

 Targionia hypophylla, Cryptomitrium tenerum., dry up com- 



