BIO
201: Botany
GYMNOSPERMS
GENERAL CHARACTERISTICS
1)
formation of Cambium - allows for growth in diameter
production of secondary tissues & wood
2)
production of Cones
hardened structures as
modified leaves = bracts
heterosporous -- separate
male & female cones
a) microsporangium produces many microspores which go
through mitotic divisions to produce Pollen
pollen = multinucleate cell with thickened wall
is the male gametophyte
b) megasporangium surrounded by protective cell layer = Integument
megasporangium + integument = ovule
female gametophyte develops inside from megaspores
3)
development of a Seed
zygote
formation and development of embryo within integument
integument
develops into a seed coat
4)
NO double fertilization
only the simple egg + sperm ---> zygote
5)
NO Fruit = lack of protective tissue surrounding the seed
group name gymnosperm = "naked seed"
TAXONOMY - 4 divisions (we will look at 3 in detail)
Division
Coniferophyta - conifers
2o
tissue with little parenchyma
leaves
needle-like, small, simple
cones dry
Division
Cycadophyta - cycads
2o tissue with much parenchyma
leaves palm-like,
compound
cones dry
Division
Ginkgophyta - maidenhair tree
2o tissue with little parenchyma
leaves fan-like
with dichotomous branching
cones small,
fleshy
Division
Gnetophyta - gnetophytes
2o tissue with little parenchyma
leaves simple,
like in angiosperms
cones small,
fleshy
DIVISION CONIFEROPHYTA
WHERE FOUND: mainly temperate and higher elevations of tropics
HABIT:
all shrubs or trees, including:
tallest: 374 ft coastal redwood
largest:
34 ft diameter sierra redwood
longest lived: 4844 year bristle cone pine
all the above found in California and/or Oregon
MORPHOLOGY:
Leaves are
typically evergreen, scale-like or needle-like
Plants produce two types of shoots
Long Shoots = regular branch
Short Shoots = side branch which contains a cluster of leaves
cluster = Fascicle
with
injury to long shoot, the short replaces
REPRODUCTION:
Male cone or microsporangiate cone composed of central axis +
attached microsporophylls
2 microsporangia per microsporophyll
Microspore Mother Cell divides
by meiosis to produce microspores which divide by mitosis
to produce pollen
outer walls with extensions make it look like Mickey Mouse
are actually
wings to aid dispersal (nice
picture, fig. 22.5)
pollen is the male gametophyte - consists
of 4 cells:
1 generative cell -----> eventually produce the sperm
1 tube cell ----> directs pollen tube development
2 prothalial cells ----> nothing
pollen release as a result of elongation of the male cone
Female cone or megasporangiate cone
each megasporophyll with 2 Ovules on upper surface of a Scale
Megaspore Mother
Cell divides by meiosis to produce megaspores which
divide by mitosis to produce the female gametophyte
female gametophyte formed by mitosis w/o cytokinesis
eventually the 1-2 Archegonia develop per ovule
at
micropylar end -- each with an egg
Pollen dispersal by wind -
commonly in
spring, pines are worst here in SC, covering everything with yellow in March
Pollen germination -
pollen tube develops into micropyle & to nucellus
during elongation generative nucleus divides to produce 2 sperm
one
sperm fertilizes egg
Zygote & development -
mitosis to 16 cubic cells = Proembryo stage (4
layers of 4 cells)
the 8 cells nearest micropyle elongate
8 other cells end out near center of ovule
one of the 4 pairs near center develops + divides faster to become the embryo
Mature seed - several components
1) Seed Coat (from integument)
2) Wing (tissue of megasporophyll scale)
3) Embryo (from zygote)
4) Female Gametophyte Tissue (tissue surrounding archegonium)
Mature embryo - several components
1) Plumule - embryonic shoot apex
2) Cotyledons - "seed leaves" (first photosynthetic leaves)
3) Hypocotyl - stem below cotyledons
4) Radicle - embryonic root
TIMING
OF REPRODUCTION:
Pines:
pollination in early spring (February to March in SC)
fertilization a year later (very slow development)
seeds mature in later summer of second year
TOTAL TIME = 1.5 years
Red Cedar in SC:
fertilization shortly after pollination
seeds mature by fall of first year (7-8 months)
ECONOMIC
USE OF CONIFERS:
lumber
resin to produce turpentine & other solvents
resin produced by tree as defense against insect damage
DIVISION CYCADOPHYTA (Cycads)
WHERE
FOUND: tropics and temperate
in US common in Florida and California
HABIT:
have unbranched vertical trunk - most less than 1 m tall
stem mostly of parenchyma - little support
terminal crown of long, leathery, compound leaves (palm-like)
REPRODUCTION:
sporophyte plants dioecious
Sporophylls in compact clusters = Cone
Microsporangia on scale-like microsporophylls
many microsporangia per microsporophyll
many pollen grains per microsporangium
Megasporangia on scale-like megasporophylls
typically in cones, some with individual sporophylls
fewer than 10 megasporangia per megasporophyll
Timing: pollination to fertilization = 4-6 months
pollination
to seed = 1 year
DIVISION GINGKOPHYTA (maidenhair tree)
only one species - Gingko biloba
WHERE
FOUND:
first found as a fossil in 1800's
later found around temples in China -- never found in wild
now commonly grown in many cities, pollution tolerant
HABIT:
leaves fan-shaped
have dichotomous branching venation
distinct long & short shoots
REPRODUCTION:
Microsporangiate "cone" not really a cone
a loose cluster of 10-20 pairs of microsporangia
Megasporangiate "cone" reduced
a single pair of naked ovules on a long stalk
Pollination by wind, fertilization shortly afterwards
Fleshy cones
produced by fall (fig. 22-11b
fleshy part is the outer layer of the integument
due to
Butanoic acid, stinks like doggy do-do (and Romano cheese)