Plant development
When the animal is born (or hatches from its egg), it has all its body parts and from that point will only grow larger and more mature.
However, both plants and animals pass through a phylotypic stage that evolved independently[2] and that causes a developmental constraint limiting morphological diversification.
[citation needed] Once the embryo germinates from its seed or parent plant, it begins to produce additional organs (leaves, stems, and roots) through the process of organogenesis.
[8] Branching occurs when small clumps of cells left behind by the meristem, and which have not yet undergone cellular differentiation to form a specialized tissue, begin to grow as the tip of a new root or shoot.
Secondary growth results in widening of a root or shoot from divisions of cells in a cambium.
This directional growth can occur via a plant's response to a particular stimulus, such as light (phototropism), gravity (gravitropism), water, (hydrotropism), and physical contact (thigmotropism).
[10] Endogenous hormone levels are influenced by plant age, cold hardiness, dormancy, and other metabolic conditions; photoperiod, drought, temperature, and other external environmental conditions; and exogenous sources of PGRs, e.g., externally applied and of rhizospheric origin.
[citation needed] There is variation among the parts of a mature plant resulting from the relative position where the organ is produced.
The smaller and more succulent the plant, the greater the susceptibility to damage or death from temperatures that are too high or too low.
[11] Plant structures, including, roots, buds, and shoots, that develop in unusual locations are called adventitious.
Adventitious roots and buds usually develop near the existing vascular tissues so that they can connect to the xylem and phloem.
In stems with secondary growth, adventitious roots often originate in phloem parenchyma near the vascular cambium.
Redwood (Sequoia sempervirens) trees often develop many adventitious buds on their lower trunks.
They are a type of natural vegetative reproduction in many species, e.g. many grasses, quaking aspen and Canada thistle.
[citation needed] Coppicing is the practice of cutting tree stems to the ground to promote rapid growth of adventitious shoots.
Adventitious rooting may be a stress-avoidance acclimation for some species, driven by such inputs as hypoxia[13] or nutrient deficiency.
Another ecologically important function of adventitious rooting is the vegetative reproduction of tree species such as Salix and Sequoia in riparian settings.
[14] The ability of plant stems to form adventitious roots is utilised in commercial propagation by cuttings.
[citation needed] Adventitious roots and buds are very important when people propagate plants via cuttings, layering, tissue culture.
Propagation via root cuttings requires adventitious bud formation, e.g., in horseradish and apple.
Leaf primordium is initiated by the suppression of the genes and proteins of the class I KNOX family (such as SHOOT APICAL MERISTEMLESS).
These verticils follow an acropetal development, giving rise to sepals, petals, stamens and carpels.
[16] The identity of the organs present in the four floral verticils is a consequence of the interaction of at least three types of gene products, each with distinct functions.
Plants use floral form, flower, and scent to attract different insects for pollination.
