1G8 



PLANT MORPHOLOGY 



\e\wt\\ the central cell dividing to form a primary neck canal cell and a 

 primary ventral cell (Fig. 135D). As a result of additional transverse 

 divisions, the primary neck canal cell gives rise to a vertical row of neck 

 canal cells, most commonly either four or eight in number, while the 

 primary ventral cell divides transversely to form the ventral canal cell 



and egg (Fig. ISSS-C). , « , u a 



By this time the archegonium has become distmctly flask-shaped, 

 the slender neck being sharply marked off from the bulbous venter. In 



E ^-"T^ F ^-1 G 



Fig 135. Development of the archegonium of Marchaidia polymorpha, X600. A, 

 division of initial into an inner and outer cell; B, appearance of three vertical walls in the 

 outer cell; C, formation of cover cell and central cell from the primary axial cell; D, forma- 

 tion of primary neck canal cell and primary ventral cell from the central cell; E and F, 

 later stages, with two and four neck canal cells; G, nearly mature archegonium, with egg 

 and ventral'canal cell derived from the primary ventral cell; H, cross section of very young 

 archegonium, showing primary axial cell surrounded by primary wall cells ; I, later stage, 

 .showing six neck cells surrounding a neck canal cell. 



all the Marchantiales the neck consists of six vertical rows of jacket cells 

 surrounding the canal (Fig. 135/). The canal cells disorganize, forming 

 a mass of mucilage through which the sperms can swim (Fig. 133B). 

 The egg is fertilized within the venter of the archegonium, which enlarges 

 to form the calyptra, the embryo developing within (Fig. 133C). In all 

 the Marchantiales except Riccia, an involucre arises around the arche- 

 gonia. In Asterella, Marchantia, and several other genera an additional 

 envelope, the pseudoperianth, arises after fertilization and generally 

 becomes very conspicuous (Fig. 139). 



Sporophyte. Riccia displays the simplest sporophyte among the 

 Bryophyta. In its development, the fertilized egg divides by a trans- 

 verse wall, resulting in two cells approximately equal in size (Fig. 136). 



