This is an overview of the major stages of development in intact plants, particularly in the annual, terrestrial angiospermous crops in which growth habit is determinate. The morphological changes associated with these stages are more distinctive and their occurence are quite easily predictable in this group of plants.
These developmental stages also occur in perennial crops such as fruit trees, but various stages are repetitive and it may take a long, indefinite time for natural death to set in. One of the oldest living, erect and single-trunked tree in the world, a bristlecone pine (Pinus longaeva, syn. Pinus aristata var. longaeva) which was discovered by Edmund Schulman in California, USA in 1958 was then established to be 4,600 years old by ring count (Schulman 1958). Also, according to Watada et al. (1984), overlapping of development stages is more pronounced in horticultural crops.
In mango (Mangifera indica), an entire tree may be physiologically ready to produce flowers. But an adjacent tree within the same orchard may have parts in various growth stages. In the latter the tree may have branches with most shoot tips having mature leaves and fully developed but dormant apical buds which, when properly induced, will readily undergo floral bud break. But other branches on the same tree may be producing vegetative flushes of growth and are unresponsive to floral induction.
Further, the exact commencement and duration of any stage of development can exhibit wide variation depending on plant genotype and environmental conditions. Even in rice, there is a difference between early and late maturing varieties (Ishizuka 1973).
With a few exception in plants, a single-celled zygote forms after fertilization, or syngamy, in which a haploid nucleus in the egg cell within the embryo sac (female gametophyte or megagametophyte) fuses with a haploid sperm nucleus from a germinated pollen. This zygote soon undergoes growth through a series of cell division and cell enlargement and ultimately transforms into a multicellular embryo in the seed.
This embryo is likened to a miniature plant within the seed. It possesses all the potential for developing into a mature plant, but is temporarily in dormant or arrested growth. Just like a mature plant, it has a root and shoot. Called the radicle, this root is described as an embryonic root because it is a part of the embryo. It is also referred to as a rudimentary root, from the root word “rudiment” which means small or tiny, a mere blob of a structure that is imperfectly developed. The embryonic shoot, called epicotyl, is likewise described as rudimentary. (click here to read Parts of a Seed)
With all the necessary environmental requisites, a small and relatively simple seed germinates. With time, it completes various stages of development and transforms into a complex mature plant having multiple organs. Finally, its overall size and weight could be several hundred or thousand times more than that of the seed, or even more.
In rice, a seed germinates and produces a seedling, the seedling continues to increase in volume, height and complexity and ultimately becomes mature, the mature plant produces inflorescences (panicle) and spikelets, and each spikelet transforms into a fruit (caryopsis) which encloses a seed. When the seeds mature in the annual crops, the entire plant soon dies.
But how much exactly is the gigantism potential of an individual seed? How many times may the original weight of a seed be multiplied in the mature plant? It would be enlightening to find, or otherwise produce, a tabular comparison of the many plant species. Here’s one example:
According to USDA (2011), sequoia trees have small seeds: 5,600 seeds weigh only about 1 ounce, or 28.3 grams (moisture content is not given). This means that one seed weighs about 0.005 gram or five-thousandth of a gram. A common tablespoon, which can hold about 10 ml or 10 grams of water, would hold around 2 million seeds if compacted!
On the other hand, the total weight of the General Sherman giant sequoia (Sequoia giganteum) at California’s Sequoia National Park, popularly known as the world’s biggest single-trunked tree, had been estimated at more than 1,000 tons (Feininger 1968).
Now let us do the mathemethical derivation. One thousand (1,000) tons is equivalent to 1 million (1,000,000) kilograms or 1 billion (1,000,000,000) grams. Assuming that the General Sherman tree originated from a single seed weighing 0.005 gram, the growth increment by weight (= 1,000,000,000g ÷ 0.005g) would be a staggering 200-billion fold at least!
>>> Continuation: The Major Stages of Development in Plants