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. PTER1DOPHYTA 



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. 



