Tag: reproduction

After arriving at the wall of the ovary, the pollen tube enters the ovule either through the micropyle or by some other route. The entrance of the pollen tube through the micropyle is the normal condition and is known as porogamy. In some cases the pollen tube enters the ovule through the chalaza(chalazogamy e.g., Casuarina), or through integuments (mesogamy e.g. Cucurbita).

In the given figure A-central cell, B-egg nucleus, C-plasma membrane, D-synergid, E-filiform apparatus, F-male gametes, G-vegetative nucleus.

The body of the ovule consists of a mass of parenchymatous cells named nucellus. It is equivalent to megasporangium $(2n)$. Megaspore mother cell or megasporocyte is a diploid$(2n)$ cell which undergoes meiosis to form a linear tetrad of four haploid megaspores (n). Normally, the chalazal megaspore is the functional megaspore while the other three degenerate.

In many aquatic plants with emergent flowers, pollination occurs by wind or insects, e.g., lotus, water lily, water hyacinth.

One Microspore mother cell after meiosis produce 4 pollen grains.

The microspore or pollen grain is the first cell of male gametophyte. The microspore starts dividing and it is known as precocious. 

The growth of organisms includes both differentiation and development. Differentiation is a process by which, less developed cells become more developed and advanced. Development is the process of growth and change of an organism.