Biology Today — December 2017

Affinities of Bryophytes with Algae

• Terrestrial plants found in
  shady and moist habitats.


• Thallus is usually
  dichotomously branched.


• Pores and stomata are present.


• Asexual reproduction absent
  but some species multiply by
  vegetative means.


• Sexual reproduction is
  oogamous.


• Sex organs are multicellular
  and have a protective covering
  (jacket) of sterile cells.


• Zygote forms embryo.


• Mostly aquatic.


• Filaments unbranched or show
  regular or irregular branching.


• Structures like pores and stomata
  are absent.


• Asexual reproduction is common
  and takes place by zoospores,
  aplanospores or akinetes.


• Sexual reproduction is isogamous,
  anisogamous or oogamous.


• Sex organs are usually unicellular
  and do not have a covering of
  sterile cells.


• Zygote does not form embryo.


• Presence of thalloid
  and gametophytic
  plant body.


• Autotrophic nature of
  plants.


• Presence of
  chlorophyll-a, b, a-and
  b-carotene.


• Starch as reserve food
  material.


• Absence of vascular
  tissues.


• Dependence on water
  for fertilisation.

Algae Bryophytes

PTERIDOPHYTES

• Pteridophytes are seedless vascular plants, i.e., vascular cryptogams having sporophytic main plant body and inconspicuous
  gametophyte. They are called as “Botanical snakes’’, evolved after amphibians (bryophytes).

General Characteristics

• They grow in a variety of habitats but mostly they are terrestrial plants that thrive well in abundant moisture and shade while
  some flourish well in xeric conditions.


• The sporophytic plant body is differentiated into true roots, stem and leaves.


• On the basis of leaf structure, pteridophytes may be microphyllous (having simple leaves with single vein, which do not form
  leaf gaps in the stem stele), e.g., Equisetum and megaphyllous (having pinnatified leaves with complex sereis of veins that
  form prominent leaf gaps in the stem stele), e.g., Pteris.


• The branching of the stem may be dichotomous type or monopodial.


• Pteridophytes show presence of vascular tissues, i.e., xylem and phloem. In xylem, true vessels are absent while in phloem,
  companion cells and sieve tubes are absent.


• The vascular system of pteridophytes varies in different groups showing stelar system ranging from simple protostele, siphonostele
  or a dictyostele.


• They reproduce asexually by means of spores, produced in small capsules called sporangia. Leaves bearing sporangia are called
  sporophylls which may be widely scattered or clustered in definite areas and structures called cones or strobili.

Fig.: Some common pteridophytes

Strobilus

Stem

Root

Leaves

Rhizophore

Selaginella

Leaves

Stem

Root

Lycopodium

Strobilus

Equisetum

Adiantum

Rhizome

Petiole

Pinnules

Sterile

shoot

Fertile

Branch of shoot

unlimited growth

Branches of

limited growth

Strobilus

Node

Internode

Tubers Rhizome

Root