GINKGO
- Ginkgo, Linnæus, Mantissa, ii. 313 (1771); Bentham et Hooker, Gen. Pl. iii. 432, 1225 (1880); Masters, Jour. Linn. Soc. (Bot.), xxx. 3 (1893).
- Salisburia, Smith, Trans. Linn. Soc. iii. 330 (1797).
Trees, several extinct and one living species, bearing fan-shaped, fork-veined leaves on both long and short shoots. Flowers dioecious, arising from the apex of short shoots, which bear at the same time ordinary leaves. Male flowers: catkins, 3-6 on one shoot, each being a pendulous axis bearing numerous stamens loosely arranged. Stamen a short stalk ending in a knob, beneath which are 2-4 divergent anthers, dehiscing longitudinally. Female flowers, 1-3, more or less erect on the shoot, each consisting of a long stalk, which bears an ovule on either side below the apex. The ovule is sessile, straight, surrounded at its base by an aril or collar-like rim,[1] and naked (i.e. not enclosed in an ovary). Fruit: a drupe-like seed (sessile in the small bowl-shaped little developed aril) consisting of an orange fleshy covering enveloping a woody shell, within which, embedded in the albumen, lies an embryo with 2-3 cotyledons. The albumen is covered by a thin membrane which is only adherent to the woody shell in its lower part. Two embryos often occur in 1 seed, and of the 2 ovules only one is generally developed into a seed.
Ginkgo was formerly considered to belong to the Coniferæ, but recent investigations show that it is distinct from these, and is the type of a Natural order Ginkgoaceæ, which has affinities with Cycads and ferns. The seeds resemble closely those of Cycads, and at the end of the pollen tube are formed two ciliated antherozoids which are morphologically identical with the antherozoids occurring in ferns. Ginkgo, however, is a true flowering plant, as it produces seeds, and is a gymnosperm, since it bears ovules which are not enclosed in an ovary.
The extinct species have been found in the Jurassic and succeeding epochs. Gardner[2] considers the specimens which have been found in the white clay at Ardtun in the Isle of Mull to be specifically identical with Ginkgo biloba.
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