On the Nature and Origin of so-called “Chichi” (nipple) of Ginkgo biloba, L.

Abstract

Ginkgo lii"lolm, the single living type of the Salisburias, stands, as we know, a.lone, a perfect stranger, in the midst of recent vegetable forms."* It is a d~cidnous tree, one of the exceptional CHses among conifers, * Solms-Laubach, Fossil Botany. ** Sohns-Laubach states in his Fossil Butany "The tree, unknown in the wild state and µreserved only in t.he groves of Chinese temples, seems to have been kept from extinction by the care of priests." But what caused the extinction of the wild plants of this species, which now flourishes in tolerably wide ranges of climate is a matter of qnestion. The two thoughts can Le snggested here in this respect. First, tlie important parts (endosperm and embryo) of the seeds are eaten by man in large q11antit1es; secon(l, there may have been tl,e extinction of animals that largely feed on the pulpy portions of the seeds and are the chief agencie~ for the clistribntion of the seeds. I have offen seen crows hold Ginkgo seeds between theil' beaks, bnt whether they actually feed on the' pulpy portions of the seed s very doubtful. At any rate, it is certain that crows have contributed very little to the distribution of the seeds of Ginkgo.

The anatomy of the chi-chi of Ginkgo biloba suggests a mode of elongation growth that is an alternative to growth driven by an apical meristem

“…Instead, the tip of the chi-chi is composed of fusiform cambial cells that weave amongst each other, as do the differentiated cells derived from them. The U-shape of the growth rings found at the tip in longitudinal sections (Fujii 1895) supports the idea that chi-chi arise as localised sites of hyperactivity in the cambium of the tree trunk or branch and that this hyperactivity persists at the tip as the chi-chi continues to develop. It also creates the growth differential required for anisotropic elongation growth of this cylindrical structure.…”

“…Nor do the parenchymatous ray cells of the secondary phloem of the ginkgo trunk seem able to form meristematic zones for chi-chi development, as they do in the development of adventitious roots, for example (Carlson 1938). However, if the reports of Fujii (1895) and Li and Lin (1991) are correct, then the development of small, more regular meristematic cells (perhaps originating from the rays) may occur when the apex of a chi-chi enters the soil and, hence, adventitious roots are initiated. The production of such roots, which in G. biloba do not seem to have any unusual structure (Voronin 1964) and include a typical root cap (which is absent from the tip of the chi-chi) suggests that the aerial chi-chi of G. biloba could be rhizophores.…”

“…In longitudinal section, the growth rings extend around the apex in the form of a ''U'' (Fujii 1895). The growth increments thus lie one upon the other like numerous overlapping thimbles of increasing size.…”

“…1,000 years) may be bedecked with chi-chi that, at such an advanced stage of a tree's life, look like woody stalactites (Handa et al 1997). The first external sign of chi-chi formation is a swelling that resembles a callus or burl (Fujii 1895;Senata 1990Senata /1991Li and Lin 1991;Snigirevskaya 1994). The chi-chi then grows vertically downwards.…”

“…Another curious feature is that the centre of the chi-chi contains ''fleck-like'' structures (Li and Lin 1991). These may be what Fujii (1895) thought of as apical buds that had somehow become internalised within the secondary tissue.…”