Chapter 7: Leaves
concepts
bud, spines
provide protection
tendrils
support
fleshy leaves of bulbs
storage
External structure of foliage leaves
most obvious function is photosynthesis
leaf blade:
flat light harvesting portion also called lamina
dorsal surface
blade's lower surface
ventral surface
upper side; usually smooth
petiole
hold the blade out into the light
sessile leaf
type of leaf blade
when leaves are small or very long and marrow, there may be no petiole
simple leaf
compound leaf
has a blade of just one part
has a blade divided into several individual parts
Vein
bundle of vascular tissue within a leaf
reticulate venation
the netted pattern in basal angiosperm and eudicots
parallel venation
the veins runs side by side with few obvious interconnections in monocots with long , strap-shaped leaves
abscission zone
cells of it involved incutting off the leaf when its useful life is over
Internal structure of foliage leaves
mesophyll
vascular tissue
Epidermis
petiole
Flat, thin foliage leave, optimal for light interception
have a large surface through water can be lost
transpiration
water loss through the epidermis
can be serious problem is soil is dry, root cannot replace water
waterproof and translucent
allows entry of carbondioxide
ground tissue interior to the leaf epidermis
Palisade parenchyma
layer of cells along the upper surface of most leaves
main photosynthetic tissue of most plant
spongy mesophyll
lower portion of leaf permits carbondioxide to diffuse rapidly away from stomata into all parts of leaf's interior
A eudicot leaf usually has one large midrib
lateral veins emerge from midrib and then branches into narrow minor vein
Bundle sheath: many fibers arrange as bundle in leaf
minor veins are important for releasing water from xylem and loading sugar into phloem
midrib and lateral rib involve in conduction
Bundle sheath extension: help give rigidity to the blade and provide an additional water to moves from bundle out to the mesophyll
part of leaf and are transition between the stem and the lamina
contain fewer stoma and trichome
leaf traces: branches from stem vascular bundles and diverge towards the petiole
stipules: in many species, the pwtiole bears two small flaps of tissue at its base called stipules.
Initiation of development of leaves
basal angiosperm and eudicots
Monocots
leaf primordium
At the base of meristem, cells just interior to the protoderm grow outward called leaf primordium
Grows so rapidly that it becomes taller than the shoot apical meristem
As leaf primordium grows upward, it increases the thickness, establishing the bulk of midribs
initiated by the expansion of some shoot apical meristem cells to form a leaf primodium
Apical meristem become the part of perimodium give hoodlike shape
Morphology and anatomy of other leaf types
spines
bud scale
tendrils
leaves with kranz anatomy
leaves of conifer
Sclerophyllous foliage leaves
insect traps
Succulent leaves
Permits plant to survive in desert
Thick and fleshy
reduce the surface to volume ratio and favors water conservation
mesophyll are transparent and contain very few air spaces
Produce more sugar by photosynthesis
Soft, flexible and edible
less amount of sclerenchyma
leaves are sclerophylls
thick cutivle and their epidermis and hypodermis have thick walls
most of them contain unpalatable chemicals
always simple never compound, have only a few form
provide protection
small, rarely compound
petiole is either short or absent
tougher and waxier
modified leaves of axillary buds
no blade and are needle shaped
no mesophyll parenchyma or vascular tissue is present
Another form of modified leaf
grows indefinitely
Contain cells that are capable of sensing contact with an object
response by sensing solid objects and growing around them.
have special metabolism called c4 metabolism
lack palisade parenchyma and spongy mesophyll
Have prominent bundle of sheaths composed of large chlorophyllous cell
Ability of leaves to trape and digest insect
grows in habitat poor in nitates and ammonia.
by digesting insects, plant obtain nitrogen they need for amino acid and nucleotides
two types
active trap
passive trap
moves during capture
incapable of movement
eg: leaves of sundew
upper surface of foliage is covered with glandular trichomesthat secrete a sticky digestive liquid
trichome and lamina are able to sense the present of insects
has numerous stomata and vascular bundles as well as mesophyll
eg: pitcher leaves of Nepenthes
thin, parenchymatous and capable of photosynthesis
lamina is tubular and secrets a watery digestive fluid