PTERIDOPHYTA 397 
Relationship of ferns. In possessing an alternation of sporo- 
phyte and gametophyte generations the ferns resemble the liver- 
worts very closely. Moreover, the thallus of a fern is very similar 

Fig. 444. A single spo- 
rophyll of Lycopodium, 
with sporangium on the 
upper surface near the 
base. (x9) 
to that of some of the simple liverworts. 
The greatest difference between the liver- 
worts and the ferns lies in the develop- 
ment of the sporophytes. In some of the 
simple liverworts the sporophyte consists 
of only a single sporangium without a 
stalk, while in the majority it lacks chloro- 
phyll and is composed of a sporangium, 
a stalk, and an absorbing organ, the foot. 
In both of these cases the sporophyte is 
entirely dependent on the gametophyte 
for nourishment. In the highest order of 
the liverworts, the Anthocerotales, the spo- 
rophyte is more complex. In <Anthoceros 
it has stomata of the type found in higher 
plants and a considerable development of 
assimilating tissue containing chloroplas- 
tids. It thus manufactures food instead 
of being entirely dependent on the gametophyte, as in the simple 
liverworts. In the ferns the sporophyte is much more highly 
specialized than in any 
of the liverworts. 
In 
the first stages of its 
growth the sporophyte 
of a fern develops a foot 
and is dependent on the 
gametophyte for nour- 








| | 
Rae area 
ESS earl Cestelaet: 
SEER TS ES TIS 
ROSA SORA BONI RA rN 
REPT RETRY As 
Sip ELIS 
SO 
ishment; but it soon yg, 445. Cross section of aleaf of Lycopodium. 
_ produces a stem, roots, (x 105) 
and leaves and becomes 
independent. In all the liverworts the gametophyte is the domi- 
nant stage in the life history. In the ferns the sporophyte, and 
not the gametophyte, is the dominant stage. 
