GINKGO, jInk'g6 (Japanese, from Chinese gin-hing, silver apricot, front yin, silver ± hing, apricot). A genus of plants represented by a single living species, which is the sole survivor of an important ancient group of gymnosperms known as the Ginkgoales. The Ginkgo biloba, or Salisburia adiantifolia, as it is sometimes called, is the well-known maidenhair-tree of cultivation, a popular name suggested by the fact that the leaves resemble those of the ordinary maidenhair fern (Adiantum). It has been cultivated for centuries in China and Japan as a sacred tree in connection with temple groves, and it has become common in ornamental cultivation in all civilized countries. It was supposed to be unknown in the wild state until its recent discovery in cer tain forests of Western China.
The tree has the general habit of a conifer, with central shaft and wide-spreading branches. It is recorded that it sometimes reaches a height of nearly 100 feet, and a trunk circumference of more than 25 feet. The characteristic leaves have long and slender petioles, with broad, wedge shaped, and variously lobed blades, and a dis tinctly forking vein system. The leaves are also deciduous, a very rare habit among gymno sperms. The spore-bearing organs—that is, the stamens and ovules—are borne upon short, spur like shoots, the stamens being in loose, catkin-like clusters, while the ovules usually occur in pairs at the summit of a long stalk. As a rule but a single one of the pair of ovules develops into the mature seed, a development which occurs whether fertilization takes place or not.
Until recently ginkgo was included among the conifers, but further knowledge of its structure has caused it to be set apart as a group by itself, equal in rank to Cycadales, Coniferales, and Gnetales, the other three living groups of gymno sperms. Prominent among the recent discoveries in connection with ginkgo has been the discov ery of ciliated (hence motile) male cells, identi cal in general character with those discovered in the cycads (q.v.). The embryo is an exception
among gymnosperms, since it does not develop the usual suspensor, but the fertilized egg di rectly produces the embryo proper. As in the cycads, the embryo develops two cotyledons, and between them there is a very conspicuous plu mule (shoot-bud). Ginkgo also shares with cycads the feature that its seed becomes plum like, a testa with fleshy outer and stony inner layers being organized. Often without pollina tion, and hence, of course, without •ertilization, the seed attains its usual size, and the two lay ers of the testa are developed. The starchy ker nel of the seed has an almond-like flavor, and is eaten, after slight roasting, by the Chinese.
The ginkgo was introduced into the United States toward the close of the eighteenth cen tury, and, because of its symmetrical shape and freedom from attacks of injurious fungi and in sects, it has come into favor as an ornamental and street tree. It is hardy as far north as Massachusetts, and at Washington, D. C., it grows quite well, several streets being planted with this species. Where employed as a street tree, only staminate specimens should be planted, so as to escape the annoyance of the falling dis agreeable smelling fruits in autumn.
Ginkgo is a very ancient genus, since it prob ably grew during Carboniferous time. An ances tral type, with lobed leaves, Ginkgophyllum, has been found in the coal measures of Great Britain and in the Permian deposits of the Ural. The genus Ginkgo itself has been found in the Per mian and Jurassic rocks of Northern Europe and Australia, and it enjoyed an almost universal distribution during Tertiary time. Several allied genera, Baiera, Rhipidopsis, Dichranophyllum, and Trichopitys, have been described from those formations.