266 INTRODUCTION TO BOTANY 
capsule in which the asexual spores are formed is a complex 
structure. The stalk upon which it is borne is known as the 
seta, Which means “ bristle” or “hair.” In the capsule itself the 
cap which covers the tip is known as the calyptra, which means 
“hood.” The calyptra is the old archegonium wall that was 
carried upward by the developing stalk. Beneath the calyp- 
tra is the mouth, or peristome, of the capsule, and over the 
mouth is an easily removed lid, the operculum. Beneath this 
lid peculiar teeth (fig. 203, D and Z) surround the mouth, and 
through these teeth the spores are dropped or thrown as 
changes in moisture cause the teeth to move in and out. 
This elaborate arrangement is thought to secure thorough 
distribution of the asexual spores of the mosses. 
251. Alternate stages in the life of the mosses. It is evident 
that in the mosses sexual and asexual reproduction are limited 
to «distinct parts of the plant. A moss spore, when it ger- 
minates, produces not the part of the plant from which the 
spore grew, but the other part. Asexual spores germinate 
and produce protonema, from which the leafy shoot grows 
by means of buds; the sex spore, or odspore, germinates and 
produces the leafless stalk, upon which grows the capsule in 
which asexual spores are formed. It is customary to speak 
of that part of a plant which produces the asexual spores as 
the sporophyte (spore plant), and of the part that produces 
the sex spore as the yuetophyte (gamete plant), or the part 
of the plant which produces the sex cells. The sporophyte is 
therefore the asexual generation of the moss, and the gameto- 
phyte the sexual generation, and they alternate in completing 
the life round of the whole plant. This relation of the two 
phases is spoken of as the alternation of generations. The fact 
that the protonema and the leafy shoot are distinct structures 
dovs not make a third phase in the alternation, for the reason 
that there is no spore intervening between them. Also, the 
term witernation, as used, refers only to sexual and asexual 
generations, and not to cases such as that of the wheat rust, 
where the asexual phase appears in several different forms. 
