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Plant Parts

There are three basic structures on plants and various modifications of them. The three structures are stems, leaves, and roots. A stem is formed from the epicotyl, the portion of the embryo above the cotyledons (the seed leaves); it has a shoot apex, the growing tip, around which leaves develop. Leaves are formed from small stubs formed on the side of the growing tip, and generally develop into flattened structures. Roots, on the other hand, are formed from the hypocotyl, the portion of the embryo below the cotyledons.

Flowers are thought to be elaborate structures formed from leaves highly modified to promote pollination. The sepals, petals, stamens, and pistils are thought to have evolved from leaves. The fruit is a further development of parts of the flower, generally the pistil, the female portion of the flower, to promote dispersal. Like flowers, fruits are thought to have been derived from leaves. Seeds and pollen are the only parts of flowering plants that cannot be traced back to a stem, leaf, or root. They are derived from the male and female parts of more primitive plants.

Botanical Freaks

Abnormal growth, caused by disease, genetics, or human manipulation, is far from unusual in the plant world. Three common forms are:

Fasciation: A stem or root that is abnormally flattened or sometimes develops into a hollow tube (ring fasciation). Cockscomb (Celosia cristata) is a fasciated form of the species Celosia argentea. In this case, the inflorescence has become abnormally flattened and resembles a cockscomb.

Chimera: A structure or tissue that is formed from two genetically different sources. Some chimeras are the result of grafts in which a branch is formed from tissue from the root stock and the grafted stem growing together. Vinca minor 'Variegata' is an example of a chimera.

Galls: A structure formed in response to insect, nematode, mite, or fungal infestations. The galls often are home to the invader for a portion of its life cycle. Oak trees often have a large number of ball-shaped galls formed by wasps. They appear to be so normal a part of the plant at times that botanists in the past have mistaken them for a type of fruit.