Reproduction
Pine Cones
Pine cones are a layer of woody scales, they are designed to protect and disperse seeds. Pine tree reproduction starts with the development of pine cones on a mature tree. The cones are produced in early spring, with both male and female cones developing on the same tree.k here to edit.
Female Pine Cones
Female cones house the eggs, and at first, they are greenish in color and tightly closed in order to protect the eggs. The cones are covered with a sticky substance which allows pollen to hold fast to the cone and push its way in. The pollen develops a tube that slowly digs deep into the cone, finally reaching and fertilizing the eggs which lie at the base of the cone's scales. By the time the seeds are fully formed, the female pine cone will have hardened and dried into the familiar brown cone shape.
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(The Pollen) Male Pine Cones
Male pine cones are usually long, soft strands called catkins. The purpose of the male pine cone is to disperse the pollen, which travels on the wind. Once the pollen is dispersed, the cone drops from the tree.
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Fly away, Seeds
Pine cone seeds have tiny wings, which, when the seeds are released from the cone, help them fly through the air on the wind. Many don't land on fertile ground, or are eaten by animals. But a lucky few land on rich soil, sprout and eventually grow into pine saplings.
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Stages of Reproduction
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- Male cones give rise to microspores, which produce pollen grains, while female cones give rise to megaspores, which produce ovules.
- The pollen tube develops from the pollen grain to initiate fertilization; the pollen grain divides into two sperm cells by mitosis; one of the sperm cells unites with the egg cell during fertilization.
- Once the ovule is fertilized, a diploid sporophyte is produced, which gives rise to the embryo enclosed in a seed coat of tissue from the parent plant.
- Fetilization and seed development can take years; the seed that is formed is made up of three tissues: the seed coat, the gametophyte, and the embryo.
- Wind or foraging animals generally disperse pine seeds into the environment. The seed germinates following stimulation by certain environmental signals, such as exposure to light or tempature changes.
Environmental Conditions for Reproduction
Grow in average, medium moisture, well-drained soils in full sun. Tolerates some light afternoon shade, particularly in hot summer climates.
Life Cycle
The male strobilus is composed of many modified leaves, called microsporophylls, which are spirally arranged about a central axis. Each microsporophyll has two microsporangia attached. Microsporangia are organs that contain microsporocytes, immature pollen grains. The microsporocytes develop into pollen grains with four cells each. The four cells of the pollen grain are haploid, in that each contains one set of chromosomes. Thus, the pollen grain of pines is a multicellular haploid tissue, and is the male gametophyte. In the spring time, the male strobilus releases pollen into the wind, and then shrivels up and dies.
The female strobilus is larger than the male strobilus. It is composed of many scales (modified leaves) which are spirally arranged about a central axis. Each scale has a sterile bract and two ovules, egg-forming structures, attached to it. The ovule consists of two types of tissues, the nucellus and its surrounding integument. A special pore, called a micropyle, passes through the integument to the nucellus.
The female strobilus is larger than the male strobilus. It is composed of many scales (modified leaves) which are spirally arranged about a central axis. Each scale has a sterile bract and two ovules, egg-forming structures, attached to it. The ovule consists of two types of tissues, the nucellus and its surrounding integument. A special pore, called a micropyle, passes through the integument to the nucellus.