Download Investigative study of angiosperms morphology - Bij Javia

Investigative study of angiosperms
morphology
[On plant stems]
Bij Javia
Preface
The following project is an investigative project on angiosperms morphology
where we were required to analyze characteristics of stems and understand the
modifications of the same.
Acknowledgement
I would like to thank many people who have contributed to the completion of this
project. My biology teachers have especially helped me by providing guidelines
and giving helpful tips on how to go about the project. Many others have also
helped me in collecting the pictures. I sincerely thank them all.
Angiosperms
Angiosperms, also known as angiospermae are the most diverse group of land
plants. Though they are seed producing plants like gymnosperms, angiosperms
produced enclosed seeds. These are flowering plants and produce fruits
containing seeds. Some prominent characteristics of angiosperms are : flowers,
which are the reproductive organs of the plant and also most distinguishing
feature; stamens as the female reproductive organ; anther, the male reproductive
part, producing smaller pollen grain which aids in easy dispersal; and
endospermic seeds.
The body of angiosperms can be divided into two fundamental parts: Root
system and Shoot system
The root system grows downwards into the soil and anchors the plant. It also
absorbs water and essential minerals from the soil. On the other hand the shoot
system comprising of the stem and the leaves grow upwards. It helps in synthesis
of food and its translocation to various parts of the plant.
The root system:
The root is the non green descending axis of the plant that normally grows
downwards into the soil. It develops from the radical and is the first structure that
comes out from the germinating seed. It is positively geotropic.
The shoot system:
The shoot is generally an above ground, aerial, erect, ascending axis of the plant
body which develops from the plumule of the embryo. It is usually positively
phototropic. It is differentiated into nodes, internodes and bears leaves, branches
and flowers.
Monocot plant
Inflorescence
Node
e
Leaf blade
Internode
Leaf sheath
Picture taken from internet
Common name: rice
Scientific name: Oryza sativa
Family: Poaceae
Dicot Plant
Picture taken from internet
Common name: tomato
Scientific name: Solanum lycopersicum
Family name: Solanaceae
Monocot vs. Dicot
Stems
Stems develop from the plumule of the embryo of a germinating seed. The stem
bears nodes and internodes. The regions of stem where the leaves are borne are
called nodes and the portions between two nodes are called internodes. Stem
shows negatively geotropic growth.
Characteristics of plant stems
The stem is the ascending portion o the plant and is the direct prolongation of the
plumule.
The young stem is green and carries out photosynthesis
It bears both vegetative and floral buds it ends in a terminal bud.
It has distinct nodes and internodes.
It is positively phototropic
Functions of stem:
It provides support for the main body of plant
It supports leaves in such positions so that they can capture maximum of sunlight
and flowers and fruits to maximize pollination and seed dispersal.
It is flexible and withstands forces exerted by winds and helps the plant to remain
upright.
It allows transport of water, sugars and other dissolved substances to various
parts of the plant.
In some plants stems form the organ where food can be stored.
In some plants stems form adventitious roots
In plants like cactus, stems form the main photosynthetic organ and also stores
water. It is therefore possible for the leaves to be reduced to spines to cut down
water loss through transpiration.
Forms of stem
1. Erect stem:
a.caudex/columnar: it is unbranched, erect, cylindrical, and
marked with scars of fallen leaves.Example:-palm
palm
b.culm: Jointed stem with slid nodes and hollow
internodes.Example:-Bamboo (Gramineae)
Bamboo
c.Deliquescent:Branched stem found in
trees like Banyan, Mango, Neem etc.
Banyan
d.Excurrent: cone shaped tree.Example:-pines
2.Weak stems:
a.Triling/Trailor:It is a weak stem that spreads over the
surface of the ground without rooting at the nodes.Example:Evolvulus, Tridax
Wood sorrel
i.
Prostate/ procumbent: stem trails on the ground and lie prostate.
Example:-Evolvulus and oxalis(wood
sorrel)
ii.
Decumbent: stem trails for some
distance and then tends to rise at its
apex. Example:Tridax, Portulaca
tridax
iii.
Diffuse: Branches of the stem spread out in all directions on the ground.
Example:boerhaavia
b.Climbers: Stems which attach themselves to nearby object by means of some
special devices like hooks, tendrils, and are known
as climbers. Examples: bougainvillea(by hooks),
wild pea(by tendrils)
Wild pea
c. creeping stem/Creepers: These stems grow
horizontally on the ground and gives off roots at
each node.
Modifications of stems:
A.
Ariel modification:
1. Stem tendrils: it is a slender, spirally coiled, thread like structure which helps
the plant to climb. When it comes in contact with the neighboring object it coils
round it and thus attaches the plant to the object. Examples: grapes/grapevine,
passiflora, gourds
(cucumber,pumpkins,watermelon)
2. Stem thorn: It is a hard usually straight and
deep seated structure with vascular
connections. It functions as an organ of
defense. Examples: pomegranate,
bougainvillea, Carissa,etc.
carissa
[prickles and hooks: these develop only from
the cortex and epidermis and found at nodes or internodes. They help in climbing.
They are exogenous in origin. Example: Rose, Smilax ]
3.Phylloclade: the stem is modified into a flat,
fleshy and green leaf-like structure which has a
succession of nodes and internodes. Leaves are
modified into spines or scales to check
transpiration and the function of photosynthesis
is taken up by the stem. They often retain water.
Examples: opuntia, euphorbia, etc.
opuntia
4.Cladode: This is a green, cylindrical/flattened
stem branch of limited growth. However unlike phylloclade these have only a
couple of internodes. Leaves are either reduced to scales or modified into spines.
B.Sub ariel modification:
1.Runner: in these stems roots develop on the lower side
and leaves at the upper side from the nodes. Example:
cynodon dactylon(doob grass), oxalis
Doob grass
2.Stolon: In it branches develop from the lower part of
the main stem and grow for some distance like an arch
and finally touch the ground to give rise to new shoot.
Example: Fragaria(wild
strawberry), Jasmine,
Peppermint
strawbery
3.Sucker: In it the main stem grows in the soil but branches develop from the
nodes and comes out from the soil. Example: mint, Pineapple, Chrysanthemum
4.Offset: Generally these occur in aquatic plants which have fragile stem.
Internodesof offset are small and thicker and each node bears a rosette of leaves
and a tuft of roots. It is also known as aquatic runner. Example: Eichhornia
C.Underground modification:
This type of modification generally occurs for food
storage and vegetative propogation.
1.Tuber: The tips of branches becomes swollen in
the soil. Eyes are found on them which are axillary
buds and covered with scaly leaves.
Example:Potato
ginger
potato
2.Rhizome: It is fleshy stem which grows horizontally
in the soil. Small nodes and internodes are found on it
which are covered by scaly leaves. Example:ginger,
turmeric
3.Corm: It is a condensed structure which grow vertically under the soil surface.
Example: colocasia, saffron
4.Bulb: Stem is highly reduced and disc like and surrounded by numerous fleshy
leaves. Many roots arise from its base.
Example: onion, garlic. The fleshy leaves of
onion and garlic store food.
Conclusion
The project has helped me gain practical knowledge of the topics printed in the
text books. It has helped me gain better understanding of the features and
identifying characteristics of different plant species like for example
differentiating a moncot plant from dicot plant.
I have also learned about the modifications of the plant stems and how that helps
the plant to survive. The shear variety of modification adopted by the plants are
amazing and awe inspiring when one understands that this is what that has led t
widespread distributions of angiosperms.
Bibliography
The information has been collected from :
Wikipedia
ISC biology text book
Biology magazines like biology today
The images are taken by:
Myself
From internet
Remarks