TAXONOMY 
287 
stalk, and forms a foot or absorbing process. In growing upward 
the sporogonium ruptures the neck of the archegonium and carries 
it upward as the covering of the capsule, or calyptra. The calyptra 
is thrown off before the spores are matured within the capsule. 
The upper part of the capsule becomes converted into a lid or oper¬ 
culum at the margin of which an annulus or ring of cells forms. The 
cells of the annulus are hygroscopic and expand at maturity, throw¬ 
ing off the lid and allowing the spores to escape. This completes 
Pig. 155.—Protonemata of a moss bearing young gametophyte bud. {Gager.) 
the asexual or sporophyte generation. The spores falling to the 
damp soil germinate into protonemata, thus completing the life 
cycle in which is seen an alteration of generations, the two phases, 
gametophyte alternating with sporophyte. 
DIVISION III.—PTERIDOPHYTA 
The most highly developed cryptogams showing a distinct alter¬ 
nation of generations in their life history. They differ from the 
Bryophytes in presenting independent, leafy, vascular, root-bearing 
sporophytes. 
