MENDELS EXPERIMENT ON HEREDITY

Mandel chose pea plant for his experiment due to its few characteristic features .

Short life cycle and high reproduction .

Self pollination due to presented of hermaphrodite .

Homozygous plants due to self pollination .It is easy to get pure line for several generation .

Visible seven pairs of contrasting characters.

The varieties can be crosspollinated bising emasculation method .

Mendel selected 22 varieties of pea out of 34 collected varieties .

He choose if pairs of contrasting characters for study these were-

EMBRYOGENY IN MONOCOTS

 After the resting period the zygote or oospore elongates and then divides by transverse division forming two cells be basal cell and terminal cell.

The basal cell remains towards the micropylar end do not divided further and produces a large swalled vesicular suspensor cells .It may functions as haustorium .

The terminal cell divides by another transverse wall forming two cells. 

The top cell after a series of divisions forms plumule and a single cotyledon .

The cotyledons is called as scutellum and it grows rapidly and pushes the terminal plumule to one side .The plumule comes to lie in a depression .

The middle cell undergoes repeated divisions and forms hypocotyl and radicle .

The middle cell also adds a few cells to the suspensor .

In some monocots e.g. in cereals ,both plumule and radicle are covered by sheaths developed from the scutellum called as coleoptile and coleorhiza respectively .

EMBRYOGENY IN DICOTS

In dicots the zygote elongates and then dividual by a transverse wall into two unequal cells i.e. basal suspensor cell and terminal embryo cell.

The suspensor cell divides transversely a few times to form a 6-10 celled suspensor .The suspensor helps in pushing the embryo in the endosperm .

The upper most cell of the suspensor towards the micropylar end forms haustorial cell while the lowermost cell of the suspensor towards the termimal  cell is called hypophysis .

The haustorical cell function as hausforium and the hypophyics gives rise to radicle and root cap.

The terminal embryo cell under goes two vertical and one transverse division to form eight cells arranged in two tiers .It is the the octant stage of pro-embryo .

The lower tier of 4-cells give rise to plumule and cotyledons while the upper their of 4-cells near the suspensor gives rise to hypocotyl .

The  octant pro-embryo divides periclinally to form outer single layer of dermatogen or protoderm from which the epidermis arises .

The inner cells divide further forming periblem internal to the dermatogen and plerome in the untre 

The ground meristem produces cortex and pith where as procombium gives rise to stele.

Initially the embryo is globular and undifferentiated .

With continuous growth the globular pro-embryo becomes heart-shaped due to the development of two premordials of  cotyledons.

Subsequent development gives rise to the dicot embryo which is horse-shoe shaped . 

SIGNIFICANCE OF DOUBLE FERTILIZATION

It is a common characteristics of angiosperm in which both the male gametes take part in fertilization .

Female gametophyte stops its growth at eight nucleate stage further growth continues after double fertilization .

It helps in the formation of seed and fruit .

Their is recombination of maternal and paternal characters .

The PEN formed during triple fusion develops into primary endosperm cell and it provide nourishment to the developing embryo and also to the germinating seed .

It is necessary for the  formation of viable seeds. 

ORNITHOPHILY

 The mode of pollination performed by birds is known as ornithophily .

Thus the flower involved for this are called as ornithophilous flowers.

Butea monosperma callistemon bombox agave .

These flowers show following characters 

The flowers are large ,showy , brightly coloured i.e. red ,orange or blue.

Flowers are scentless or odurless .

The flowers secrete abundant watery nectar made up of sugar .

The pollen grains are sticky .

The floral parts are commonly leathery .

Two common types of tropical pollinating birds are sunbeids and humming berds some other birds are- crow ,bulbul ,parrot and mynah.

ENTOMOPHILY

 It is most common type of zoophily where the pollination is carried out through the agency of insects like- moths , butterflies , wasps , bees ,etc .

The flower are called as entomophilous flowers they show following characteristics -

Flower are generally large if small they become conspicuous by their grouping .

They are showy or brightly coloured .

Where petals are not conspicuous other parts becomes show 

Example- Bract- Bougainvillea

                 Leaves- Euphorbia palcherrima

                Sepal - Mussuenda

                Stamen - Mimosa

Flowers contain nectar glands and pleasant fragnonce to attract insects.

These is no wastage of pollen grains so less number of  pollen grains are produced .

The pollen grains are spiny , heavy and surrounded by a yellow oily sticky substance called pollen kit .

The stamens are inserted .

Stigmas are often inserted , sticky ,unbranched etc .

Example - Minoso- touch me not

HYDROPHILY

The pollination which is accomplished through the agency of water is called hydrophily.

The flowers pollinated by water are known as hydrophilus flower.

Hydrophilous plant are ceratophyllum  ,valisnaria ,hydrila etc.

Hydrophilous flower shows following adaptation .

Flowers are small and inconspicuous .

Perianth and other floral oarts are unwettable.

Flowers are with out bright colours, pleasant frogrance and nectar glands .

Pollen grains are naked with coating and are light in weight .

Stigma is long sticky but unwettable .

Flowers are usually unisexual and open under water or at the surface of water .