page_title: Plant development
section_title: Morphological variation during growth
hierarchical_section_title: Plant development / Growth / Morphological variation during growth
context_page_description: Important structures in plant development are buds, shoots, roots, leaves, and flowers; plants produce these tissues and structures throughout their life from meristems located at the tips of organs, or between mature tissues. Thus, a living plant always has embryonic tissues. By contrast, an animal embryo will very early produce all of the body parts that it will ever have in its life. When the animal is born, it has all its body parts and from that point will only grow larger and more mature.
  According to plant physiologist A. Carl Leopold, the properties of organization seen in a plant are emergent properties which are more than the sum of the individual parts. "The assembly of these tissues and functions into an integrated multicellular organism yields not only the characteristics of the separate parts and processes but also quite a new set of characteristics which would not have been predictable on the basis of examination of the separate parts."
context_section_description: Plants exhibit natural variation in their form and structure.  While all organisms vary from individual to individual, plants exhibit an additional type of variation.  Within a single individual, parts are repeated which may differ in form and structure from other similar parts.  This variation is most easily seen in the leaves of a plant, though other organs such as stems and flowers may show similar variation. There are three primary causes of this variation: positional effects, environmental effects, and juvenility.
  There is variation among the parts of a mature plant resulting from the relative position where the organ is produced.  For example, along a new branch the leaves may vary in a consistent pattern along the branch. The form of leaves produced near the base of the branch differs from leaves produced at the tip of the plant, and this difference is consistent from branch to branch on a given plant and in a given species.
  The way in which new structures mature as they are produced may be affected by the point in the plants life when they begin to develop, as well as by the environment to which the structures are exposed. Temperature has a multiplicity of effects on plants depending on a variety of factors, including the size and condition of the plant and the temperature and duration of exposure. The smaller and more succulent the plant, the greater the susceptibility to damage or death from temperatures that are too high or too low. Temperature affects the rate of biochemical and physiological processes, rates generally (within limits) increasing with temperature.
  Juvenility or heteroblasty is when the organs and tissues produced by a young plant, such as a seedling, are often different from those that are produced by the same plant when it is older.  For example, young trees will produce longer, leaner branches that grow upwards more than the branches they will produce as a fully grown tree.  In addition, leaves produced during early growth tend to be larger, thinner, and more irregular than leaves on the adult plant.  Specimens of juvenile plants may look so completely different from adult plants of the same species that egg-laying insects do not recognize the plant as food for their young. The transition from early to late growth forms is referred to as 'vegetative phase change',
  but there is some disagreement about terminology.
caption: Variation in leaves from the giant ragweed illustrating positional effects. The lobed leaves come from the base of the plant, while the unlobed leaves come from the top of the plant.
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