io8 



MORPHOLOGY 



Sporophyte. The sporophyte of Antbocerotales deserves special 

 attention on account of its structure and on account of its degree of 

 independence (figs. 239, 240). The outline of its development is as 

 follows: the fertilized egg divides by a vertical 

 wall. (trans verse in other bryophytes) ; subsequent 

 transverse and vertical walls result in three tiers 

 of four cells each; the three tiers produce foot, 

 seta, and capsule. The innermost tier develops 

 a foot which penetrates the thallus by rhizoid- 

 like processes, and finally becomes a large bulbous 

 structure (fig. 241). The middle tier, which also 

 contributes somewhat to the foot, develops the 

 so-called intermediate zone, corresponding in 

 position to the seta of other groups. It is a 

 region of active cell-division, continually adding 

 to the capsule below, which thus becomes an 

 elongated structure by basal growth (as distinct 

 from apical growth). This growth may not con- 

 tinue long, resulting in a short capsule (Noto- 

 thylas, fig. 240); or it may continue long enough 

 to result in a much elongated linear capsule 



rlGS. 239 240 An- 



tA0cmrfa/a:a 3 9,thallusof (Anthoceros, fig. 239). Where the sporophyte 

 Anthoceros bearing sporo- (sporogonium) emerges from the thallus, a 

 phytes; the two sporo- tubular sheath is developed around its base by 



phytes to the right show 



the dehiscence by two the tissue of the thallus. 



valves, leaving the colu- Capsule. The development of the outermost 



mella exposed; 24 o, thai- ^ j capsule formation is especially noteworthy. 



lus of Notothylas bearing J J 



sporophytes. By a series of transverse walls a number of tiers 



of cells is produced, and periclinal walls cut off a 



peripheral layer of cells (amphithecium) inclosing a group of central cells 

 (endothecium). Among the Marchantiales and Jungermanniales there 

 is the same setting apart of two regions, the amphithecium producing 

 the capsule wall, and the endothecium developing the sporogenous 

 tissue. Among the Anthocerotales, however, the two regions develop 

 in a very different way. The endothecium does not develop sporogenous 

 tissue, but forms a central axis of sterile tissue (columella}, which in 

 Anthoceros usually shows sixteen cells in cross section. By periclinal 

 walls, the amphithecium becomes two-layered, and the inner layer is the 

 sporogenous tissue, which thus caps the columella in a domelike layer; 



