BRYOPHYTA 



189 



cover cell, primary neck canal cell, and primary ventral cell. The cover 

 cell later divides by one or two vertical walls; the primary neck canal cell 

 gives rise to four or sometimes six neck canal cells; and the primary ven- 

 tral cell produces the ventral canal cell and the egg (Fig. 154F, G). Just 

 previous to fertilization the cover cells and canal cells break down, leaving 

 the egg in a cavity below the surface of the thallus (Fig. 15-iH). 



Fig. 155. Embryos of Anthocerotales, X300. A, yonng emhryo oi Anthoceros fusiformis; 

 B, slightly older enibrjo of Anthoceros piinctatus, showing differentiation of amphithecium 

 and endothecium; C, embryo of Megaceros, showing two sporogenous cells cut off from 

 amphithecium; D, later stage, showing further development of sporogenous tissue. 



Sporophyte. In Anthoceros the first division of the fertilized egg is 

 vertical, the second transverse, and the third vertical at right angles to 

 the plane of the first division (Fig. 155A). A fourth division occurs 

 transversely in the upper part of the embryo, resulting in three tiers of 

 four cells each. The upper tier produces the capsular region, the middle 

 tier an intermediate zone, while the lower tier forms the foot. In the 

 development of the capsular region, which occurs very early, the amphi- 

 thecium is cut off from the endothecium by periclinal walls (Fig. 1555). 

 The latter forms the columella, an axis of sterile tissue. The amphithe- 

 cium soon becomes two-layered, the inner layer giving rise to the spo- 

 rogenous tissue and the outer layer to the sterile wall (Fig. 155C, D). The 

 derivation of the sporogenous tissue from the amphithecium rather than 

 from the endothecium is very characteristic and stands in marked contrast 

 to the condition in the other Hepaticae. In some species of Notothijlas, 

 however, the endothecium does not produce a sterile columella but, 

 instead, gives rise to the sporogenous tissue. 



