SCIENCE.
��495
��I I
��THE GINKOO-TRBE.
As event of considerable interest to hotaniats has just occurred at Washington in the flower- ing, for the first time, of two of the ginkgo-treos io the U. S, Imtanic garden.
In [tassing the grounds on Satnrday evening. May 6, after the gales were closed, my atten- tion was altraeted to a tree standing Just inside the enclosure, which, though as yet nearly leafless, was loaded with stamtnate aments borne in terminal clusters on very short branch- lets al! along the branches, even down to the base of the larger ramifications. A glance showed that it waa a ginkgo, though I had neiTr seen one in flower before ; and, after examining it sufllciently. I went away, and was obliged to wait until Monday morning before I could notify the superintend en I, Mr. W. R. Smith, and institute a search for other trees in the same condition.
Presuming that, as is usually the case in pul.ilic gardens and parks, all the trees in the city would also be males, so that no opiwrtu- nil'y would exist for witnessing the IVuiting of this tree, I was most agreeably dieappoint<Kl when I learned that Mr. A. L. Schott had found another tree in flower in the same en- closure, and that this tree was a female. I thei-eupon carefully in9|>ected both these trees, and found that aothesis was so nearly synchro- nous in the two sexes that I was able on the oth to pronounce them ready for fertilization. But as ihey stand some seventy-five yards apart, with the superintendent's bouse and other ob- stacles between them, it was evident that this could not take place unaided ; and accordingly, with the hearty co-operation of Mr. Smith, the work of artificial pollinization was undertaken. This has been repeated several times at differ- ent hours of the day, anil so thoroughly per- formed that it is hoped the result will be aacuessful,* and that iraSt will be borne this season.
The so-called Japanese ginkgo,' or maiden- hair tree (Ginkgo biloba, Linn. ; Sahsburia adiantifolia, Smith), is one of the most interest- ing trees that have been introduced into the landscape plantations of Europe and America. Although possessing deciduous foliage and broad green leaves, it nevertheless belongs lo
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��the Coniferae, though its affinities with the rest of titat family are anomalous, being closest with the yew tribe, .\n examination of its leaves shows them to be wholly unlike those of any other phenogamous plant. They are del- toid in outline, and the fine nerves that run trom the narrow base to the broad apex fork several times in their course, after the manner of ferns. In fact, a ginkgo leaf very closely resembles a much enlai^ed and thickened pin- nule of the maiden-hair fern ( Adiantum) , — a resemblance which not only suggested to Smith the specific name adiantifolia, but has caused the tree to be popularly called in some locali- ties the maiden-hair tree.
A study of the paleontological history of this remarkable plant reveals the fact that it is an archaic form, and the sole survivor of an Otherwise extinct type of vegetation which had numerous representatives in the remote geo- logic iiast. The Salisburia adiantoides of Un- ger, found in the upper miocene of Senegal, is not essentially different from the lii-ing spe- cies ; and Professor Heer detected it again in the miocene strata of Greenland. In ISSl I was so fortunate as to obtain from Laramie strata at Point of Rocks Station, Wyoming Territory, a form which, except for its smaller leaves, appears to be identical with the linng one : and in 1883 1 found in Fort Union strata, on the lower Yellowstone, a slightly dirt'crent form, with larger leaves, showing no lobes, proving that the present living form has come down to us. almost unchanged, from a period as remote at least as the cretaceous age. But other and distinct forms are found in the cre- taceous, and still others, showing greater and greater divergence, as far back as the Jurassic ; those of the oolite bearing clear evidences of having been derived from a series of still older, digitate -leaved forms ( Jeanpaulia, Baiera, etc. ) whose relationship with the ginkgo was not suspected until these intermediate ones had been brought to light by Heer from the meso- zoic rocks of Spitsbergen and Siberia. In fact, until recently these earlier Jurassic forms, which had been long well known, wei'e from their nervation referred to the family of ferns ; as, indeed, a fossil leaf of the ginkgo would probably be now, if the living plant were un- known.
But even this is not all. By another series of far more ancient forms (Trichopitys, Psyg- mophyllnm, Xoeggcrathia) , this persistent tj'pe may be traced still farther back, even across the boundary between mesozoic and paleozoic time, until, in the great carboniferous flora, it has been connected, almost without
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