Female cone in pinus | reproduction in pinus | life cycle of pinus and angiosperms

Female Cone:
Female cones are produced in pairs or in clusters in the axil of the scale leaves. The female cones mature very
slowly. The first year young cone is small (1-2 cm in length),soft,compact and red-green in
colour. The second year cone is comparatively large (5-8 cm in length),woody,compact and
green in colour.
The fully matured third year cone is much larger(15-60 cm in length),woody, loose and brown in colour.Here
megasporophylls are separatedfrom each other due to the elongation of the cone axis.
The female cone of Pinus represents a compound shoot; it is a complicated structure.The female cone is
composed of a central axis on which 80-90 megasporophylls,axillary to bract scale/scale leaves, are arrange
spirally .
The bract scale and ovuliferous scale thus form a seed-scale complex.
A single megasporaphyll consists of two types of scales:
(a)a large woody ovuliferous scale or seminiferous scale bearing two ovules on the adaxial surface,and
(b) a bract scale or cone scale on the abaxial surface .

Initially, the ovuliferous scale is much smaller than that of bract scale, but after pollination it becomes larger than the bract scale. The ovuliferous scale is a thick, large, woody, roughly triangular and brownish structure. Its upper thick exposed part is known as apophysis. In the mature cone, the tip of the apophysis becomes the 'umbo" . There are two separate vascular traces, one supplies to the ovuliferous scale and the other to the bract scale . There is no separate vascular trace for ovule.

The development of megasporangium (ovule) is of eusporangiate type i.e., an ovule develops from a group of superficial cells of the ovuliferous .Pinus: Median LS. of a mature ovule scale.
Ovule
The ovules of Pinus are anatropous, unitegmic and crassinucellate . The single integument is free from the nucellus except at the chalazal end. There is a fairly broad micropylar tube which becomes inwardly curved during pre-pollination stages and becomes outwardly curved at the time of pollination. The integument is three-layered, the outer fleshy, the middle stony and the inner fleshy.

Gametophyte of Pinus:

The spore is the first phase of gametophyte generation. The microspore or pollen grain represents the male gametophyte, while the megaspore represents the first stage of female gametophyte which develops into a female gametophyte.

Pollination:

Pinus is anemophilous i.e., wind-pollinated. The pollen grains are dispersed and remain suspended in the air for some time. At the same time, the nucellar beak in the ovule disorganises forming a viscous sugary liquid containing glucose, fructose and sucrose. This fluid comes out in a cyclic phenomenon (24 hr. cycle) through the micropyle in the form of a pollination drop either at night or in the early hours of morning. The pollen grains are caught in the pollination drop and are collected in the pollen chamber as a result of drying off the fluid. The mouth of the micropyle is then sealed from the outer environment.
Fertilization:

The fertilisation takes place after one year of pollination. The pollen tube enters the tip of the archegonium by forcing itself between the cells of the nucellus. The pollen tube wall is disintegrated by the enzymes secreted from the egg and eventually two male nuclei are released. One of the male nuclei fuses with the egg cell and thus a zygote is formed.
Pinus species.

In two-year type, the pollination and fertilization take place in late spring of first and second year, respectively. In three-year type the pollination takes place in spring of first year, and fertilisation in the spring of third year, a lapse of two years. The seeds shed in autumn

Seeds of Pinus:

The seeds are endowed with a well- Pinus: A. LS. of seed, B. An ovuliferous scale bearing seeds, C. A seed with wing

developed wing which is thin and papery and is easily detachable at maturity . The outer fleshy layer of integument and part of ovuliferous scale contribute to the wing formation . The seeds are usually dispersed by wind. The embryo remains embedded within the endosperm.

The seeds of Pinus remain viable for a long time. The germination of seed is epigeal.
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