II 



MUSCINEyE—HEPA TIC^—MARCHANTIA CE.E 



39 



now on is essentially the same. The growth of the cells in the 

 forward part of the dorsal surface of the young thallus is more 

 active than that of the ventral side, so that they project over 

 the growing point (Fig. 9), and as the outer cells of the lateral 

 segments of the apical cell (or cells) also increase rapidly in 

 size as they recede from the growing point, the forward margin 



Fig. g.—Riccia hirta (Aust.)- Later stages of germination. A, from below, X 260 ; B, optical section 

 of A, showing apical cell x, X 520 ; C, X 85 ; r, root-hair's. 



of the thallus, seen from below, is deeply indented, and the 

 forward part of the thallus is thus occupied by a deep cavity, at 

 the bottom of which, toward the ventral side, lies the growing 

 point. This cavity is the beginning of the groove or furrow 

 found in the older thallus. 



At first the cells of the young thallus are without inter- 

 cellular spaces, but at an early period (Fig. 9, C) the outer cells 



