BIO 201: Botany

Chapter 16 of Evert & Eichhorn

Life Cycle: alternation of generations with gametophyte dominant

1) Development of enclosed sex organs
     female = archegonium
     male = antheridium
2) Sporophyte develops attached to (parasitic on) the gametophyte
3) Lack vascular tissue - must live near or in water

Three groups: (recognized at level of Division/Phylum)

Mosses Division Bryophyta
gametophyte leafy and grows vertically
some elongate water conducting tissues present
gametophyte reproductive organs not stalked
sporophyte with columnella

Liverworts Division Marchantiophyta
commonly thallose and grows flat on substrate
gametophyte develops stalked reproductive organs
sporophyte small, lacks columnella within sporangium

Hornworts Division Anthocerophyta
gametophyte thallose and grow flat on substrate
gametophyte reproductive organs not stalked
sporophyte with columnella


MOSSES (Division Bryophyta) pp. 378-387

     Leaf-like structures are not true leaves - lack vascular tissue
     Not restricted to moist habitats - but need water to grow
     distinct adult and juvenile forms to gametophyte generation
          juvenile = protonema - look like a filamentous green algae

Asexual Reproduction - three possible methods
     1) branching of "stems"
     2) formation of propagules
     3) protonema: numerous juvenile plants

Sexual reproduction - plants dioecious (fig 16-23, p. 383)
     organs produced in apex of leafy stem
          1) antheridia with surrounding modified thickened leaves (fig 16-23b)
               individual antheridia separated by paraphyses
               structures include: a) sterile jacket layer, b) stalk, c) spermatogenous tissue, and d) paraphyses
               sperm produced by mitosis
          2) archegonia without thickened leaves (fig 16-23a)
               structures include: a) neck canal cells, b) venter, c) stalk, and d) paraphyses
               egg produced by mitosis in venter
     sperm transfer by splashing rain water

Sporophyte development (check them out on p. 385)
     embryo develops a long stalk = setum
     spores produced in terminal capsule
          within capsule is columnella (central internal stalk)
          top of capsule - operculum with peristome teeth that are hygroscopic
          Note: hygroscopic means sensitive to humidity
     spores wind dispersed as peristome teeth allow dispersal
     spores germinate into juvenile plants = protonema
          highly branched filaments
          can distinguish from algae: rhizoids, developing buds

Life cycle in book: pp. 386-387; in PowerPoint: Life cycle diagram

Usual moss = Sphagnum
     grows in peat bogs which produce peat moss
     major component
     produces an acidic pH
     stems filled with many water-filled spaces which allow for water holding during drought


LIVERWORTS (Division Marchantiophyta) pp. 373-377

Morphology - thallose forms with distinct upper & lower surface
     commonly have distinct equal branching = dichotomous
     internal anatomy with photosynthetic above storage tissues
     dorsal pore for gas exchange (permanently open)
      ventral rhizoids for attachment

Asexual Reproduction - two methods (p. 375)
     1) dichotomous branching
     2) gemmae cups produce little multicellular propagules

Sexual Reproduction - stalked structures with one sex only (p. 374)
     Antheridiophores - produce antheridia on upper surface (fig 16-11a)
          each antheridium contains an outer sterile jacket layer
          produces many sperm by mitosis (with flagella)
     Archegoniophores - produce archegonia on lower surface
(fig 16-11b)
          each archegonium produces only one egg
          include: neck canal cells, venter, stalk (but NO paraphyses)
     Sperm gets from antheridium to archegonium via rain splash
          Sperm swims down neck canal to egg

Sporophyte development:
     Zygote develops into the sporophyte on gametophyte
     structures include: a) foot, b) stalk, c) capsule (fig 16-12)
         capsule includes spores (produced by meiosis) and elators (hygroscopic and aid dispersal of spores)

Life cycle in book: pp. 376-377; from PowerPoint: Life cycle diagram