112 EVOLUTION OF PLANTS 
capsule is ripe, help to distribute the spores (Fig. 
28, H). 
In contrast to the simple sporophyte of the lower 
liverworts, there is found in one group a sporophyte 
which reaches a high degree of complexity, and be- 
comes almost independent of the gametophyte. This 
reaches its highest expression in the genus Anthoceros 
(Fig. 28, D, Fig. 31,C). Here the gametophyte is very 
primitive and consists of a simple thallus composed 
of almost perfectly uniform cells, and without any dif- 
ferentiation into stem and leaves. Indeed, it represents 
almost the lowest type of the gametophyte among the 
Hepatice. A suggestion of an origin of this type of 
thallus from the Algz is seen in the single chloroplast 
in each cell, much like that in Coleochete. The sexual 
organs of Anthoceros, while on the whole like those of 
the other liverworts, are peculiar in being sunk in the 
thallus, and recall, in this respect, those of the more 
primitive ferns. 
It is the sporophyte, however, which is of the greatest 
interest. This reaches a relatively large size (Fig. 31, 
C, sp) and shows a considerable degree of independent 
growth. Between the large foot and the upper portion 
is a zone of growing tissue, which enables the sporophyte 
to grow in length as long as the gametophyte remains 
active, and from this growing zone new tissue is con- 
stantly added to the base of the sporophyte. The latter 
has its outer parts developed into a perfect assimilating 
tissue with several layers of spongy green tissue whose 
air-spaces communicate with the outside atmosphere by 
means of stomata or pores in the epidermis, precisely 
like those found upon the leaves of the higher plants. 
