The maize is monoecious and unisexual. The male inflorescence (tassel) is borne terminally and female inflorescence (cob) laterally at lower levels. Maize pollens are large and heavy and cannot be carried by a light breeze. However, the mild wind shakes the male inflorescence to release the pollen which falls vertically below. The female inflorescence has a long stigma (silk) measuring up to 23 mm in length, which projects beyond leaves. The pollens drop from the tassel is caught by the stigma.

In bisexual flowers, the stamens and stigma are arranged in such a way, that cross pollination is only possible.
Example: Gloriosa superba - the style is reflexed away from the stamen
Hibiscus - the stigma project for above the stamen.

When the pollen deposits on another flower of the same individual plant, it is said to be geitonogamy. It usually occurs in plants which show monoecious condition. It is functionally cross-pollination but is similar to autogamy because the pollen comes from the same plant

Chasmogamy	Cleistogamy
In chasmogamy, the flowers open and express its mature anthers and stigma for pollination.	In cleistogamy, the pollination occurs without opening of flowers and exposing their sex organs
Self-pollination is uncertain	Self-pollination is certain.
Depend on pollinating agents	No need of pollinating agents
Example: Hibiscus	Example: Commelina

(a) Egg - 1
(b) Secondary nucleus - 1
(c) Synergids - 2
(d) Antipodal cells - 3

The egg apparatus possess two synergids.
Synergids secrete chemotropic substances that attract the pollen tube.
Synergids also guides the pollen tube into the egg.

Pollenkitt is contributed by the tapetum and colored yellow or orange and is chiefly made of carotenoids or flavonoids. It is an oily layer forming a thick viscous coating over pollen surface. It attracts insects and protects damage from UV radiation.

(i) Bee pollen is a natural substance with high proteins, carbohydrate, and a trace amount of vitamins and minerals.
(ii) It is used as a dietary supplement as tablets.
(iii) It increases the performance of athletes, racehorses and also heals burn wounds.

The wall material sporopollenin is contributed by both pollen cytoplasm and tapetum. It is derived from carotenoids. It is resistant to physical and biological decomposition. It helps to withstand high temperature and is resistant to strong acid, alkali and enzyme action. Hence, it preserves the pollen for long periods in fossil deposits, and it also protects pollen during its journey from the another to stigma.

(i) It supplies nutrition to the developing microspores.
(ii) It contributes sporopollenin through ubisch bodies thus plays an important role in pollen wall formation.
(iii) The pollenkitt material is contributed by tapetal cells and is later transferred to the pollen surface.
(iv) Exine proteins responsible for 'rejection reaction' of the stigma are present in the cavities of the exine. These proteins are derived from tapetal cells

There are two types of tapetum based on their behavior. They are: 
Secretory tapetum (parietal/glandular/ cellular): The tapetum retains the original position and cellular integrity and nourishes the developing microspores.
Invasive tapetum (periplasmodial): The cells lose their inner tangential and radial walls and the protoplast of all tapetal cells coalesces to form a periplasmodium.

In a mature anther, the cells along with junction or the two sporangia of an anther lobe lack cellulose and lignin thickening. This region is called stomium. Stomium along with hygroscopic nature of Endothecium helps in the dehiscence of anther at maturity.

(i) Tissue culture can be carried out in any season to produce plants.
(ii) Plants which do not produce viable seeds and seeds that are difficult to germinate can he propagated by tissue culture.
(iii) Cells can be genetically modified and transformed using tissue culture.

Tongue grafting	Wedge grafting
In tongue grafting A scion and stock having the same thickness is cut obliquely and the scion is fit into the stock and bound with tape.	In wedge grafting a slit is made in the stock or the bark is cut A twig of the scion is inserted and tightly bound so that the cambium of the two is joined