It 



MUSCINE^—HEPA TIC^—MARCHANTIALES 



5S 



pressed (Fig. 19, C), so that this may account for Janczewski's 

 error in stating that the number was always four, as the nuclei 

 in unstained sections might very easily be overlooked. The 

 cover cells are somewhat smaller than in Riccia and do not 

 usually undergo as many divisions, there being seldom more 

 than six in all. In Targionia (Fig. 23, A), and Strasburger 

 ( (21), p. 418) observed the same in Marchantia, the ripe egg 

 shows a distinct "receptive spot," that is, the upper part of the 

 unfertilised egg is comparatively free from granular cytoplasm, 

 while the lower part, about two-thirds in Targionia, is much 

 more densely granular. The nucleus is not very large and has 

 very little chromatin. The nucleolus is large and distinct and 



Fig. 19. — Targionia hypophyUa. A, Longitudinal section of the apex of the thallus, 

 with young archegonia (ar), XS25; x, the apical cell; B, young, C, older arche- 

 gonium in longitudinal section; D, cross-section of the archegonium neck» X525. 



stains very intensely. As the archegonium of Targionia 

 matures, its neck elongates rapidly and bends forward and 

 upward, no doubt an adaptation to facilitate the entrance of 

 the spermatozoid. A similar curving of the archegonium neck 

 is observed in other forms where the archegonium is upon the 

 lower side of the receptacle. 



After an archegonium (or sometimes several of nearly 

 equal age) is fertilised, the growth in length of the thallus stops, 



