Development of a seed
As Arborists, our experience with trees often range from pruning fully grown specimens to preparing young saplings for planting. While not many of us are directly involved in nursery management, it is still important to know the reproductive cycle of trees for a more holistic approach towards tree care, especially if in-situ propagation of trees is part of the aim.
From ovaries to seeds
Trees reproduce through pollination, a process where pollen is exchanged between the male and female reproductive parts of a tree. Pollination can be performed by living pollinators like birds, bats and insects or via wind or water.
In flowering trees (Angiosperms), pollen is transferred from the anthers of a flower to the stigma of a flower, which usually happens through the actions of living pollinators, wind or water. Once on the stigma, the pollen grain creates a pollen tube that grows through the style and reaches the ovary, where fertilisation occurs.
In non-flowering trees (Gymnosperms), pollen grains are transferred from male cones to female cones by dispersal through wind. When this happens, the sperm from the pollen grains either move independently to the egg inside the ovule or is transferred to the egg via a pollen tube. Once pollinated, the ovule begins developing into a seed.
Anatomy of a seed
A seed is made of 3 main parts: embryo, endosperm and seed coat. The plant embryo, after fertilisation, develops over time to form a new plant. The endosperm, which envelops the embryo, provides food and nutrients for the growing embryo to utilise as it grows. The seed coat, located on the outermost portion of the seed, protects both the embryo and endosperm from damage and water loss.
Seed to a sapling
Seeds are first dispersed away from the parent plant, which can happen through 5 modes: wind, water, animals, ballistic and gravity. Once the seeds reach areas with the appropriate temperature, moisture and light, it begins to germinate, a process where the embryo develops into a seedling. This seedling will continue to grow in height, develop leaves, roots and shoots, gaining the ability to photosynthesize and no longer depend on the seed’s food reserves to grow as it gradually develops into a sapling.
Tree saplings are fragile and can easily die from water stress, uprooting, predation and disease, so great care must be accorded to them. This may include regular watering, repotting/ replanting if they are growing in an overly shallow media or environment, staking of the sapling to ensure it remains upright and light application of fertilizer to ensure its health.
With sufficient care, this small sapling will eventually grow into a large, healthy tree, bringing with it all the benefits that a tree provides!
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