268 



BRYOPHYTA 



The development of the sporogonium has been carefully studied in 

 Anthoceros by Campbell. 1 The early segmentations result in three tiers 

 composed of four cells each (Fig. 130 A): of these the lowest is derived 

 from the hypobasal half of the zygote, and it forms the main part, if 

 not indeed the whole of the foot. The highest tier gives rise to the 

 primary capsule, while from the intermediate zone derived from the 

 second tier the meristematic part of the older sporogonium is formed 

 (Fig. 130 ?:). The highest tier of four cells segments further to form 



FIG. 130. 



Anthoceros Pearsoni. Development of the embryo. X 300. A, C, E, median longi- 

 tudinal sections. B and D, successive cross-sections of embryos of about the age of A 

 and C respectively. In E the archesporium is differentiated. (After Campbell.) 



a central group of four, and a peripheral series (Fig. 130 c, D) : from 

 the former the sterile columella originates, although in all other Liverworts 

 the corresponding cells give rise to the archesporium. This, however, 

 is primarily formed in Anthoceros from the inner cells resulting from 

 periclinal division of the peripheral cells of the highest tier, and its 

 form is that of a dome completely covering the rounded apex of the 

 columella (Fig. 130 E). The columella thus initiated in Anthoceros 

 develops entirely as sterile tissue. The layer of cells immediately outside 

 it, recognised as the archesporium by their denser protoplasm, differentiates 



1 Mosses and Ferns, p. 134. 



