1. Since geitonogamy involves two different flowers of the same plant, it is genetically similar to autogamy; both autogamy and geitonogamy do not result in genetic variation in the progeny.
2. Geitonogamy and cross-pollination involve different flowers and a pollinating agent.

(i) In Vallisneria, the male flowers are released on the surface of water and female flowers reach the surface by the long stalk.
(ii) Pollen grains are protected from wetting by a mucilaginous covering.

Advantage
1. Since cleistogamous flowers are autogamous, there is an assured seed-set.
Disadvantage
1. Continued self-pollination leads to inbreeding depression.

1. Emasculation is necessary to prevent the self-pollen grains falling on the stigma.
2. Emasculation is not needed when the female parent chosen bears unisexual,  i.e. female flowers.

In wind pollinated flowers,
(i) The stamens are well-exposed, so that pollen grains are easily dispersed in wind currents.
(ii) The stigma is large and often feathery, to easily trap the air-borne pollen grains.
(iii) The pollen grains are light and non-sticky, to be transported in wind currents.
(iv) Pollen grains are produced in enormous quantity.
(v) Numerous small flowers are packed into an inflorescence.
(vi) There is a single ovule in the ovary of these flowers.

Functions of micropyle
(i) It is the passage through which the pollen tube enters the ovule.
(ii) It remains as a small pore in the seed coat and facilitates the entry of water and oxygen during seed germination.

(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.

(a) Syngamy
Syngamy refers to the fusion of a male gamete with the female gamete in the embryo sac to form a diploid zygote.
Triple fusion
Triple fusion refers to the fusion of a male gamete with the secondary nucleus (formed by fusion of two haploid polar nuclei) to form the triploid primary endosperm nucleus.
(b) Embryo development
Th'e zygote undergoes mitotic divisions during embryogeny.
The first division is transverse and results in a basal cell and a terminal cell; the basal cell forms the suspensor while the terminal cell forms the embryo proper.
It first, forms a filamentous proembryo, which later forms in sequence a globular embryo, heart-shaped embryo and then a mature embryo.

(b) Tapetum is the innermost wall layer; whose cells possess dense cytoplasm and more than one nucleus.
 It nourishes the developing pollen grains.
(c) (i) The exine of pollen grains is made of sporopollenin, which can withstand high temperature and action of strong acids or alkalies; no enzyme can degrade sporopollenin and hence, pollen grains are well preserved as fossils.
(ii) Pollen grains are rich in nutrients and hence, are used in the form of tablets as food supplements.

(i) (a) : A typical angiosperm anther is bilobed with each lobe having two theca, i.e., dithecous and a dithecous anther is tetrasporangiate having four microsporangia, two in each lobe.
ii) (c)
(iii) (c) : The tapetal layer is of great physiological significance as all the food material entering into the sporogenous tissue diffuses through this layer. Ultimately the cells of tapetal layer disorganise. Thus, tapetum makes a nutritive layer for the developing microspores or pollen grains.
(iv) (d)
(v) (d) : Tapetum secretes Ubisch bodies which get covered with sporopollenin and so increase thickness of exine of pollen grain wall. Tapetum provides nourishment to developing microspores. It also secretes callase enzyme which dissolves callose substances by which four pollens of a pollen tetrad are united, hence separating microspores or pollens of a tetrad.