268 BRYOPHYTA 
The development of the sporogonium has been carefully studied in 
Anthoceros by Campbell! 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 
Re 
FIG. 130. 
Anthoceros Pearsoni. Development of the embryo, X300. A, C, £, median longi- 
tudinal sections. 2B and D, successive cross-sections of embryos of about the age of A 
and C respectively. In Z 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 Axthoceros 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 §£). The columella thus initiated in <Amthoceros 
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. 
