280 



THE BRYOPHYTES 



caUed rhizoids (from their resemblance to roots), and delicate 

 membrane-like fringes, which draw up water from the soil like 



root hairs if the plant has 

 the land habit. The thal- 

 lus grows from a number 

 of points (Fig. 245, A, gp) 

 situated in notches at the 

 ends of lobes which fork in 

 pairs and finally split apart, 

 so that the plants multiply 

 very rapidly during the veg- 

 etative season. The sexual 

 organs are borne on the up- 

 per surface of this game- 

 tophyte, and the sporophyte 

 is a simple globular case 

 (Fig. 245, B), filled with 

 spores, which remains in- 

 closed in the base of the 

 archegonium, so that the 

 spores are not set free until 

 the decay of the plant.* 



288. The Marchantia 

 group. This large group 



FIG. 245. A floating liverwort (Riccio- 

 carpus) and its sporophyte 



A, habit sketch of the sexual plant (game- (order Marchantiales) is 



tophyte) viewed from above, showing the well represented bvthe com- 

 position of the sporophytes in lines back / 



of the growing points gp. B, section of mon liverwort (Marchantia 



a sporophyte contained within the parent p ly m0 rplia\ which grows 



archegonium, whose neck n is still pres- , . . 



ent: a, spores in groups of four (tetrads) Oil the ground in moist 



within the spore mother cells; w, remains 

 of the wall of the sporophyte 



situations. The ribbon-like 

 thallus of species of Mar- 

 chantia (Fig. 246) forks regularly, but one of the branches is 



*To THE INSTRUCTOR : These points are admirably illustrated in the large 

 floating form (Ricciocarpusnatans), which is not uncommon and is an excellent 

 type for laboratory study, although Marchantia is the form most generally used. 



