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Fertilization is the process by which fusion of the male and female gametes takes place. Fertilization involves pollen germination, entry of pollen tube into the embryo sac, release of male gametes anti-double fertilization. During pollen germination, the generative nucleus divides to form two male nuclei/gametes which are released into the embryo sac by the rupture of the pollen tube.

One of the gametes passes between the synergids and fuses with the egg cell to form the diploid zygote/oospore and the other fuses with the secondary nucleus to form the trlploldPEN/ primary endosperm nucleus. Since the male gamete participates in two fertilizations it is termed double fertilization and since the formation of the secondary nucleus is already a product of nuclear fusion it represents triple fusion. 

The roots of gymnosperms are generally tap root. In Cycas, the roots are of two typesnormal and coralloid. The coralloid roots are irregular negatively geotropic, devoid of root. These are associated with nitrogen fixing cyanobacteria. In Pinus, besides the normal roots there are the mycorrhizal roots which have fungal association in the form of mycorrhiza.

Female sex organ of Bryophytes, as well as pteridophytes, is called archegonium.

(i) Double fertilization means the fusion of one male gamete with egg cell and other male gamete with the polar nuclei, this is known as triple fusion. 

(ii) When male gamete fuses with egg cell it forms diploid zygote (2n) and when the other male gamete fuses with the polar nuclei (2n) it forms a triploid endosperm (3n). 

(iii) Endosperm is a female gametophytic tissue which provides nutrition to the embryo.

Gametophyte.

Identifying features of angiosperms: 

(i) Flowering plants show great number of diversities in habit, habitat, forms, duration of life, mode of nutrition, etc. 

(ii) The plants with stem varying from a few mm to a metre or so in height are termed as herbs, medium sized plants with woody stem are termed as shrubs and tall woody plants are known as trees. 

(iii) Plants which live for a year, or part of year are termed as annuals; which live for two years are termed as biennials and which live for more than two years are termed as perennials. 

(iv) Plants which live in extremely dry conditions are termed as xerophytes: plants living in water are termed as hydrophytes and those living in moderate conditions are termed as mesophytes. 

(v) All flowering plants have roots, stem and leaves. They also produce flowers, seeds and fruits.

(i) Cycas 

(ii) Cycas 

(iii) Gingko

Diploid sporophyte is dominant phase of Pteridophyta. 

Pteridophytes are vascular cryptogams They posses xylem and phloem tissues in their organs. They do not possess flowers and seeds.

The plant body is sporophyte differentiated into stem, root and leaves.

The leaves are sporophylls they bear spore-producing sporangia.

The sporophyte is diploid. It reproduces asexually and produces haploid spores.

The spores germinate and produce haploid gametophytes or prothallus. The gametophyte is independent and heart-shaped (In Nephrolepis).

Gametophyte is bisexual it consists of antheridia and archegonia (sex organs). They produce garnets by sexual reproduction.

Zygote or oospore is a resulting product of fertilization. It develops into the sporophyte.

In the lifecycle, there is an alternation of generation between diploid sporophyte and haploid gametophyte.

• Gymnosperm plant body is sporophyte. 
• Sporophyte consists of stem, root and leaves. Stem is unbranched in cycas. the stem bears crown of leaves at the tip. 
• The foliage leaves are pinnately compound in cycas and needlelike in conifers. Brown small non-photosynthetic leaves called scale leaves/cataphylls are present in cycas.
• In cycas, the cataphylls are thickly covered with brown hairs called ramenta.
• The foliage leaves are green. The pinnae are tough, leathery and has only midrib without veins.
• Young leaves show circinate vernation.
• The roots are inhabited by blue-green algae like Nostoc help the plant in nitrogen fixation 
• Sporophyte produces two types of spores so it is heterosporous.

The various evidences which favour the chlorophycean (green algae) origin of land plants are: 

(i) Both green algae and land plants possess the same type of chlorophylls, a and b. 

(ii) The carotenoid pigments are similar in the two group. 

(iii) Cell wall contain similar cellulose and pectic compounds in the two group. 

(iv) Starch is the common storage carbohydrate in the two group. It is made of both amylose and amylopectin fractions. 

(v) The flagella are similar in the motile forms of the two.