66 PHARMACEUTICAL BOTANY 



gonium. The base of the stalk remains imbedded in the basal portion of the arche- 

 gonium at the tip of the leafy 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 operculum at the margin of which an annulus or 

 ring of cells forms. The cells of the annulus are hygroscopic and expand at maturity, 

 throwing off the lid and allowing the spores to escape. This completes 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 genera- 

 tions, 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. 



SUBDIVISION I.— LYCOPODIALES OR CLUB MOSSES 



Small perennial vascular, dichotomously branched herbs with stems 

 thickly covered with awl-shaped leaves. The earliest forms of vascular 

 plants differing from ferns in being comparatively simple in structure, 

 of small size, leaves sessile and usually possessing a single vein. Except 

 in a few instances the sporangia are borne on leaves, crowded together 

 and forming cones or spikes at the ends of the branches. Homosporous. 



Family i. Lycopodiace^, including the single genus Lycopodium 

 with widely distributed species. The spores of Lycopodium clavatum 

 are ofEcial. 



Family 2. Selaginellace^, including the single genus Selaginella, 

 with species for the greater part tropical. Plants similar in habit to the 

 Lycopodiaceas but showing heterospory. 



Family 3. Isoetace^, including the single genus Isoetes whose 

 species are plants with short and tuberous stems giving rise to a tuft of 

 branching roots below and a thick rosette of long, stiff awl-shaped 

 leaves above. Heterosporous. 



SUBDIVISION II.— EQUISETALES 

 (The Horsetails or Scouring Rushes) 



The Fquisetales, commonly known as the Horsetails or Scouring 

 rushes are perennial plants with hollow, cylindrical, jointed and fluted 



