Page 2 - LN-CH-2[2]

 On maturity the pollen grain contains two cells, the vegetative cell and generative cell.
 The vegetative cell is bigger, has abundant food reserve and a large irregularly shaped nucleus.
 The generative cell is small and floats in the cytoplasm of vegetative cell.
 In 60% of angiosperms, pollen grains are shed at this 2-celled stage.
 In others the generative cell divides mitotically to form two male gametes before pollen grain are shed (3-
celled stage).

Economic importance of pollen grain:

 Pollen grain may cause severe allergies and bronchial afflictions.
 It may cause chronic respiratory disorders – asthma, bronchitis, etc.
 Pollen grain of Parthenium or carrot grass causes pollen allergy.
 Pollen grains are rich in nutrients hence used as pollen tablets for food supplements.
 Pollen consumptions increase performance of athletes and race horses.
 After shedding the viability depends on temperature and humidity.
 In wheat and rice the pollen grain lose viability within 30 min. of their release.
 In Rosaceae, Leguminoseae and Solanaceae they remain viable for months.
 Pollen grain can be preserved for years in liquid nitrogen (-196oC).

The Pistil, Megasporangium (ovule) and Embryo Sac:

 The Gynoecium represents the female reproductive part of the flower.
 The Gynoecium may contain single pistil (monocarpellary) or may have more than one pistil
(multicarpellary).
 Fused pistils are called syncarpous and free pistils are called apocarpous.
 Each pistil has three parts the stigma, style and ovary.
 Inside the ovary is the ovarian cavity (locule).
 The placenta located inside the ovarian cavity.
 Megasporongia or ovules arise from the placenta.
 The number of ovule inside the ovary may be single or many.

The Megasporangium (Ovule):

 Ovule is a small structure attached to the placenta of locule with a stalk called funicle.
 The body of the ovule fused with the funicle in the region called hilum.
 Hilum is the junction between the funicle and ovule.
 Each ovule has one or two protective envelops called integuments.
 Integument covered the ovule except an opening at the top called micropyle.
 Opposite of the micropylar end, is the chalaza, representing the basal part of the ovule?

Megasporogenesis:

 The process of formation of megaspores from the megaspore mother cell is called Megasporogenesis.
 In the centre of the ovule there is a mass of tissue called nucellus.
 Cells of nucellus have abundant reserve food materials.
 One cell of the nucellus towards micropylar end differentiated into megaspore mother cell (MMC).