1. In crop improvement programmes, pollen grains of the selected male parent only, are used for pollination.
2. So, emasculation of a bisexual flower is necessary to prevent contamination of the sigma with self-pollen.

The three parts of a pistil and their functions are:
(i) Stigma - it acts as the platform where the pollen grains are lodged during pollination.
(ii) Style - it exposes the stigma for easy pollination.
(iii) Ovary - it encloses the ovule(s) inside which is the female gametophyte.

Vallisneria is pollinated by water.
Water lily is pollinated by insects.
In Vallisneria, the male flowers (later pollen grains) are released on the surface of water and keep floating.
The female flowers reach the surface of water by uncoiling of the long stalk
When the passively carried male flowers/pollen grains meet the female flowers, pollination is effected.
The stalk of the female flower coils and the flower is drawn inside the water column.

A fertilized ovule undergoes the following changes in the ovary in an angiosperm plant:
Unfertilized ovule \(\rightarrow \) Fertilized ovule \(\rightarrow \)Seed
Funiculus   \(\rightarrow \) Present
Hilunf  \(\rightarrow \) Present
Integument  \(\rightarrow \) Seed coat
Outer integument \(\rightarrow \) Testa
Inner integument \(\rightarrow \) Tegmen
Chalaza \(\rightarrow \) Present
Micropyle \(\rightarrow \) Present
Nucellus \(\rightarrow \) Absent or present as perisperm
Embryo Sac:
Antipodal cells \(\rightarrow \)  Degenerate
Synergid cells \(\rightarrow \) Degenerate
Secondary nucleus \(\rightarrow \) Endosperm
Egg \(\rightarrow \) Embryo
When the unfertilized ovule undergoes double fertilization, it makes fertilized ovule and then seeds. In this process funiculus and hilum are present. Outer integument makes testa and inner integument is tegmen. Chalaza and micropyle are present but nucellus is absent, partly persish. as perisperm.
In embryo sac antipodals and synergids degenerate. The central cell makes endosperm, and the egg changes into embryo.

(i)No,it was not a wise decision.
(ii) Insecticides kill the insects.These insects are very important for plants as many of these are helpful in carrying out pollination which is very essential for fertilization and seed formation in sexually reproducing species.
(iii)No,many insecticides pollute and, being non-biodegradable, have harmful effects on living organisms

(a) Differences: 

(b) Pollen-Pistil Interaction.
The stigma/pistil has the ability to recognise the right type of pollen, i.e. the compatible pollen of the same species and rejects the wrong type of pollen grains.
It is the result of interaction between the chemical components of the pollen and those of stigma. - A compatible pollen grain starts its germination on the stigma.
The intine grows out through one of the germ pores as a protuberance.
The contents of the pollen move into this tube, i.e. the tube nucleus (nucleus of the vegetative cell) and the generative cell (or the two male gametes in those species where pollen is liberated in the three-celled stage).
The pollen tube grows through the tissues of stigma and style and enters the ovule through micropyle.
It enters the embryo sac through the filiform apparatus of one of the synergids to liberate the male gametes.
The events from the deposition of pollen on the stigma till the pollen tube enters the ovule, are collectively referred to as pollen-pistil interaction.