172 F. Cavers. 
bearing sinuses alternating with the involucres project outwards as 
ridges (Fig. 28, A and B). 
The species of Marchantia differ a good deal in the organisation 
of the carpocephalum. The simplest type is seen in M. geminnta. 
Fig. 28. Preissia commutata. A.—Horizontal section of a female receptacle, 
showing the four lobes and the alternate archegonial groups with young 
sporogonia and unfertilised archegonia. x 15. B.—Part of A, x 60, showing 
the receptacle-stalk with its two ventral rhizoid-grooves and one of the 
archegonial groups in which two sporogonia are developing. Beside the young 
sporogonia are shown four unfertilised archegonia. The outer tissue of the 
receptacle contains air-chambers, the inner tissue contains abundant starch- 
grains, and the hollow lobe is nearly filled with scales, seen in section. C.— 
Upper portion of a nearly ripe capsule in longitudinal section, showing the 
lens-shaped apical cap, the cells of which bear ring-like fibres and from which 
there project some fixed elater-like cells, x 90. D .—Lower portion of capsule 
in longitudinal section, showing the basal thickening of the capsule-wall and 
the fixed elaters occupying the bottom of the capsule, x 90. E and F.— 
Capsule-wall in surface view. E is from the upper, F from the lower portion 
of the capsule, x 90. 
Here the carpocephalum has four spreading flat branches, each of 
which is notched at the free end and hears on its underside a group 
of archegonia surrounded by an involucre, the latter being formed 
