190 PLANT MORPHOLOGY 



The foot becomes bulbous and in many species penetrates the thallus 

 by means of rhizoid-like papillae (Fig. 15G). The intermediate zone is 

 meristematic. It contributes somewhat to the development of the foot, 

 but is chiefly concerned with the elongation of the capsular region. There 

 is no seta. Notothylas has a short capsular region, the other genera a long 

 one. The young sporophyte is protected by the surrounding tissue of the 

 thallus, which grows upward with it to form a massive involucre. This 

 is later ruptiu'ed by the elongation of the sporophyte, forming a basal 

 sheath. 



The columella consists of elongated cells. It may be regarded as repre- 

 senting the beginning of a conducting system. In Anthoccros the colu- 

 mella shows about 16 cells in cross section. In the young sporophyte the 

 sporogenous tissue caps the columella in a dome-like manner. It soon 

 becomes two-layered above and then gives rise to spore mother cells. 

 Meanwhile new sporogenous tissue continues to be differentiated in the 

 meristematic region lying just above the foot (Fig. 1565). Although, in 

 Anthoccros, the sporogenous tissue generally becomes two-layered, it may 

 remain one-layered, as in Anthoccros hawaiiensis, or may become three or 

 four layers thick, as in Anthoccros hallii and Mcgaceros. In Notothylas 

 the amount of sporogenous tissue is greatly increased; in some species a 

 definite columella is not formed and the sporogenous tissue arises from 

 both the amphithecium and endothecium, or from the endothecium alone. 



The wall of the capsule becomes four to eight layers of cells thick. In 

 Anthoccros, but not in the other genera, the outer layer, constituting the 

 epidermis, develops stomata. These are not like the air pores seen in the 

 gametophyte of the Marchantiales, but resemble the stomata of the higher 

 plants. The wall layers beneath the epidermis develop chloroplasts and 

 intercellular spaces, thus becoming a photosynthetic region. 



The intermediate zone elongates constantly, adding to the capsular 

 region from below. Thus spores continue to be produced over a long 

 period. It is noteworthy that the Anthocerotales are the only bryophytes 

 whose sporophyte displays indeterminate growth. Some of the sporog- 

 enous cells become sterile, small groups of these alternating with groups 

 of spores and so tending to break up the spore mass into separate units. 

 As a rule, these sterile cells give rise to peculiar short elaters that are often 

 branched. In Anthoccros the elaters, where present, are smooth- walled ; 

 in Notothylas they have short, curved, thickened bands on their walls; in 

 Mcgaceros and Dcndroccros the elaters have spiral thickenings like those of 

 other liverworts. The capsule dehisces by splitting into two valves. 



Summary. The Anthocerotales are of phylogenetic interest in that 

 they may represent a stage of progress through which the higher plants 

 have passed in the course of their evokition. As in the Jungermanniales, 

 the gametophyte is simple and the sporophyte complex, but the complex- 



