Sexual Reproduction in Flowering Plants Test - 2

Intine forms the inner layer of pollen grains and largely composed of cellulose and pectins.

Adventive embryony is also known as nucellar embryony. Here, there may be a mega-gametophyte in the ovule, but the embryos do not arise from the cells of gametophyte. They arise from the diploid cells of nucellus or integuments.
Hence, embryo forms directly from the diploid sporophytic cells (nucellus or integuments) of ovule (other than zygote). It is sporophytic in origin.

During the development of female gametophyte, the sporogenous cell directly behave as megaspore mother cell. Diploid megasporocyte or megaspore mother cell enlarges in size and divides by meiosis (reduction division) to form a tetrad of four haploid megaspores.

The lowermost cell of the suspensor situated at the terminal end (in contact with the globular proembryo) is called hypophysis which divides by transverse and longitudinal divisions to form three tiers of cells. The cells of the inner tier, towards embryo, form the cortical initials of the radicle (embryonic root).

The transference of characters by a male gamete and its influence on the development of the endosperm is known as xenia, which was observed by Focke.

Cells of tapetum have generally more than one nucleus per cell. The binucleate or multinucleate condition arises due to fusion of two uninucleate cells of tapetum.

Nucellus and MMC are diploids. Cells of nucellus are somatic cells. Thus, diploid number of chromosomes is present. MMC is diploid and divides to produce haploid megaspores.

Microspore mother cells, megaspore mother cell and sporogenous cell all undergo meiosis to form pollen, megaspores and megaspore tetrads respectively.

Besides cellulose, the intine layer of pollen grain also consists of pectin.

In seeds of some plants like black pepper, remnants of nucellus is persistent. This residual, persistent nucellus is called perisperm.