THE FERNS 123 
green tissue enables it to utilize the carbon dioxide of 
the atmosphere. 
It is not along step from such a sporophyte as that 
of Anthoceros to that of the lower Pteridophytes. In 
the latter, owing to the 
early development of a 
root in the sporophyte, 
the latter soon becomes 
quite independent of the 
gametophyte, which is 
generally short lived, 
although occasionally it 
reaches a considerable 
size and may live for 
several years, especially 
where the sporophyte 
Fie. 31.—A, gametophyte of a fern 
fails to develop (Fig. 
31, A). 
The sporophyte in 
even the lowest Pterido- 
phytes exhibits a com- 
plexity far exceeding 
that of the highest 
(Marattia), showing a forking of the 
growing point, and the development 
of secondary buds, k; B, gameto- 
phyte of the same fern, with the 
young sporophyte, sp, attached; C, 
a liverwort, Anthoceros, with several 
sporophytes, sp, attached to the 
gametophyte, gy. The sporophyte is 
capable of long-continued growth, 
but does not develop a root, and 
hence never becomes entirely inde- 
pendent. 
moss. This is especially. 
the case in regard to the external differentiation. While 
in all Bryophytes there is very little development of 
special external members in the sporophyte, in ferns 
there are very early developed several characteristic 
external organs, viz., stem, leaf, and root. The foot, or 
absorbent organ of the embryo, is much like the corre- 
sponding organ in the moss-embryo. 
Corresponding to this development of external mem- 
