Download Lecture 11, Bot 499H/505 Secondary Growth

Lecture 11, Bot 499H/505
Secondary Growth
Formation of the secondary xylem (=wood) and
periderm (bark) systems
Primary growth
Formed at an apical meristem
Responsible for growth in length of the plant
Shoot apex
Secondary growth
• Cause of increased stem diameter
• Arises from a lateral meristem (not at the apical
meristem)
• Two lateral meristems in seed plants
– Vascular cambium
– Phellogen = cork cambium
Vascular
cambium
formation
in gymnosperm or
eudicot
Vascular cambium
in the stem
Vascular
cambium t.l.s.
Pine
Flowering plant
Cell divisions in the vascular cambium
Multiplicative = anticlinal division-adds to the
width of the vascular cambium to keep up
with the growth in diameter
Additive = periclinal division-produces the
mother cells
Tilia – two year old stem
Vascular rays are living parenchyma cells
Salix root x.s.
Primary and
secondary growth
Various keys and sites for wood anatomy
identification
• http://insidewood.lib.ncsu.edu/search
• International Association of Wood
Anatomists (IAWA)- List of microscopic
features for hardwood identification by an
IAWA Committee-Wheeler, Baas & Gasson
(eds.)- 1989
• IAWA-List of microscopic features for
softwood identification-Richter, Grosser,
Heinz, & Gasson (eds.)- 2004
Vessel elements or
no vessel elements
Juniperus
Ash
Fraxinus
Periderm
Secondary tissues
produced by the phellogen
Protective tissue
Called bark-or the bark system
Consists of 3 parts
Phellogen = cork cambium = lateral meristem
Phellem = cork-produced to outside-cells
suberized and sometimes also lignified
Phelloderm = parenchyma-like-produced
toward the inside-usually thin-walled cells
Stages in periderm formation
pl
ph
pd
ep
pl
ph
ph=phellogen
pd=phelloderm
pl=phellem
ep=epidermis
Fate of the epidermis and cuticle is to be
sloughed off the outside
of the stem as phellem
produced
Mesozoic Pteridosperms
Subdivision: Pteridospermophytina
Class: Pteridospermopsida
Order: Corystospermales-Triassic-Cretaceous
Order: Peltaspermales-Pennsylvanian-Triassic
Order: Caytoniales-Jurassic
Class: Glossopteridopsida
Order: Glossopteridales- Penn.-Triassic
Class: Pentoxylopsida
Order: Pentoxylales-Cretaceous
Lagenostoma ovule in Calymmatotheca cupule
Corystosperms
Compressions-So. Hemis.
Common now known
permineralized
from Antarctica
Leaf = Dicroidium (D)
Seeds =
Pilophorosperma
(arranged on branching
system-one seed/cupule
with micropyle extended
Pollen organ =
Pteruchus (H) terminal,
flattened segments with
pollen sacs
Bisaccate pollen
Peltaspermales
Pinnate leaves =
Lepidopteris
Seed bearing
structures =
Peltaspermum
up to 20 seeds/
cupule on peltate
head-like structures
“cupulate disc”
Pollen organs=
on Lepidopteris
foliage = Antevsia
Compression/imp.
So. Africa &
Greenland
Caytoniales
Caytonia seed &
cupule
Caytonanthus
Caytoniales
Sagenopteris leaves
Net-veined, compoundlike flowering plants?
Gymnosperm
pollinationpollen lands on
micropyle of
ovule-usu.
carried by wind
pollination droplets usually
Glossopteridales
• Southern Hemisphere mainly
• Upper Carboniferous-Permian
• The occurrence of Glossopteris leaves on all
of the southern continents gave fuel to the
theory of Continental Drift – Wegener 1910
• Leaves are common and in extensive matsplants that produced them were deciduous
(shed their leaves) and many are found in
larves (lake deposits)-so we can tell that they
were shed in the fall.
Glossopteris leaf mats
Glossopteris
Leaves have a mid-rib
composed of several veins
Net-venation
Large leaves 10-15 cm long
Spatulate
Name stands for the plant and
its leaf
Mostly known as compression/
Impressions
Permineralized material is now
known from Antarctica and
Australia
Glossopteris
net venation, multiple
mid-veins
Vertebraria- roots of Glossopteris
Glossopterids
Reproductive
structures called
“fertiligers” by
Schopf (J.M.)
Borne in the axils
of leaves or on the
leaf mid-rib
A. Ottokaria
B. Lidgettonia
C. Eretmonia
D. location of fertiliger
E. Leaves on plant
F. seed
G.Pollen grain – bisaccate-striate
Glossopterid seed bearing structures
Austroglossa
Glossopterids
• Many taxa of reproductive structures (see lab manual
for drawings of different types)
• Pollen types include-bisaccates, monolete and trilete
spores
• Therefore, this is probably a large group with a lot of
diversity and maybe there are several orders of
plants involved here.
• They all have a similar leaf and similar placement of
the reproductive parts but are very different
morphologically
• Glossopterids also have been reported from the
Jurassic of Mexico-Mexiglossa name for the leaf-little
is known about this taxon.
Mesozoic seed ferns
• All starting to enclose their seeds in cupules of
one form or another
• All cupules are not equivalent, therefore the
term “cupule” means different things in
different groups
Lyginopteridales—fused telomes-branches
Caytoniales—enrolled leaf
Peltaspermales—peltate head=leaf
Corystospermales—enrolled leaf
Mesozoic “The Age of Cycads”
Subdivision: Cycadophytina
(cycads) (U.Carb. ?)Permian-Recent
Subdivision: Cycadeoidophytina
Order: Cycadeoidales (=Bennettitales)
Order: Williamsoniales
(Jurassic-Cretaceous, cycadeoids)
Both groups had leathery fern-like leaves
Lab 15 has Mesozoic foliage types
How to tell which is which?
Macrozamia
Australia
Cycads have
circinate
vernation
Uncoiling of leaf
during
development
like ferns
Leaves leathery=
coriaceous
In cycads seeds are borne on leaves=megasporophylls
Cycas megasporophylls
Encephalartos
pollen cone
Modified leaves
also on the
pollen cones
Cycad
sperm
50,000 flagella
Large, swim
in breakdown
products of
nucellar apex
released just
above
archegonium
Shed flagella
before fusion
of gametes
Mesozoic “The Age of Cycads”
Cycadeoidea
Black Hills, South
Dakota
Collected by Cope & Marsh
late 1800’s while searching
for dinosaurs
Trunks with mantle of
protective leaf bases
(sclerotic) and in the axils of
leaves are the
reproductive structures
In Tyrell Museum of Palaeontology
Monanthesia – a cone in the axil of every leaf
Cycadeoidea structure studied
by Wieland 1906, 1916-Yale
Microsporophyll
Receptacle bearing
ovules and interseminal
scales
Burger at Field Museum Chicago
Bract
Structure is bisexual
(contains both seeds
and pollen))
Bract covered
in trichomes
microsporophyll
Receptacle
Seeds and
interseminal
scales
Two rows of
synangia on
each pinna of
microsporophyll
Cycadeoidea
reinterpreted
by Delevoryas
1960’s
microsporophyll
bract
These
structures
never opened
like a flower
How were they
pollinated?
Crepet 1970’s
beetles
seeds &
interseminal
scales
receptacle
Williamsoniella
Williamsonia
Cone Structure,
&
Receptacle
Unisexual
has only
seeds
Cycad-like foliage
Ptilophyllum
Pterophyllum & Ptilophyllum (small)
Nilssonia
Horseshoe Canyon overlook-Drumheller, AB
Cretaceous
Otozamites
Taeniopteris
Types of stomatal development in cycadophyte
leaves
Thomas and Bancroft 1913
Haplocheilic
vs.
Syndetocheilic
Guard cells develop from one initial cell in leaf epidermis
Subsidiary cells formed by surrounding
epidermal cells
Stomata in rows
Epidermal cells straight-walled
Cuticle thin
(comparatively)
Cycadales
Conifers, Ephedra
Ginkgo
subsidiary cells develop from
same initial as guard cells
stomata scattered
epidermal cells with wavy outlines
cuticle thick
Cycadeoidales
Welwitschia, Gnetum
Ginkgo
Joffre
Bridge
Australia
Horseshoe
Canyon Fm.
Drumheller
Ephedra
Gnetum
Welwitschia