302 
PLANT STUDIES 
.rh 
FIG. 276. A common 
(Polytrichum commune), 
showing the leafy gameto- 
phore with rhizoids (rh), 
and two sporophytes (sporo- 
gonia), with seta (s), calyp- 
tra (c), and operculnm (d), 
the calyptra having been re- 
moved. After SCHENCK. 
plant from which it came. This new 
leafless body consists of a slender 
stalk bearing at its summit an urn- 
like case in which are developed nu- 
merous asexual spores (Figs. 276, 292). 
This whole structure is often called 
the "spore fruit," and its stalk is 
imbedded at base in the summit of 
the leafy branch, thus obtaining firm 
anchorage and absorbing what nour- 
ishment it needs, but no more a part 
of the leafy branch than is a para- 
site a part of the host. 
When the asexual spores, pro- 
duced by the " spore fruit," germi- 
nate, they reproduce the alga-like 
body with which we began, and the 
life cycle is completed. 
In examining this life history, it 
is apparent that each spore produces 
a different structure. The asexual 
spore produces the alga-like body 
with its erect leafy branch, while 
the oospore produces the " spore 
fruit " with its leafless stalk and 
spore case. These two structures, 
one produced by the asexual spore, 
the other by the oospore, appear in 
alternating succession, and this is 
what is meant by alternation of gen- 
erations. 
These two "generations" differ 
strikingly from one another in the 
spores which they produce. The 
generation composed of alga -like 
body and erect leafy branch pro- 
