BRYOPHYTA 



171 



additional walls in the upper part of the embryo, the foot, seta, and cap- 

 sule are differentiated. In other genera, such as Marchantia, the first 

 division of the fertilized egg is followed by the appearance of two vertical 

 walls at right angles to each other in both the upper and lower segments, 

 thus forming octants, as in Riccia. Additional walls in all three planes 

 produce a globular embryo rather than an elongated one (F'ig. 139), 



An early formation of periclinal walls in the capsular region cuts off the 

 amphithecium from the endothecium, the former forming the capsule 



B C 



Fig. 139. Development of the embryo of Marchantia polymorpha. A, four-celled stage, 

 X320; B, slightly later stage, X320; C, older embryo, showing the foot (/), seta (s), capsule 

 (c) with sporogenous tissue differentiated, pseudoperianth (p), and calyptra (a), X200. 



wall and the latter the sporogenous tissue (Fig. 138£'). In Riccia the 

 sporogenous tissue is derived equally from both halves of the embryo. In 

 practically all the other genera, whether the embryo is of the filamentous 

 or of the octant type, apparently only the upper half contributes to the 

 sporogenous tissue, the lower half giving rise to the foot and seta. The 

 foot anchors the sporophyte and absorbs nourishment. The seta elon- 

 gates, especially after the spores ripen, pushing the capsule through the 

 calyptra. 



In most genera, except Riccia, some of the potentially sporogenous cells 

 of the young capsule give rise to elaters, while the others directly become 

 spore mother cells. In Marchantia, however, the sporogenous ceils 

 greatly elongate, some remaining undivided to form elaters, the others 

 dividing transversely a number of times to form vertical rows of spore 



