232 



GNETACEyE. 



[GYMNOGE.NS. 



Okber LXXVI. GNETACE/E.— Joint Firs. 



Guetea:, Blumc, in Ann. Sc. 2. Ser. 2. 105. (1834).- 



Endl. Gen lxxix. 



-Gnetacese, Lindl. in Bot. Reg. 1686. (July, 1834) ; 

 . Meisner, p. 352. 



Diagnosis. — Gymnogens with repeatedly branched jointed stems, simple net-vemed leaves, 

 l-cellcd anthers opening by pores, and lite membrane next the nucleus protruded. 

 Small trees very much branched, or sarmentose shrubs, secreting watery, not resinous 



_r 



Fig. CLXI1I. 



matter, with opposite or clustered branches, and 

 thickened separable articulations. Leaves oppo- 

 site, entire, with anastomosing, reticulated veins ; 

 sometimes very minute and scale-shaped. Wood 

 with the ligneous tissue marked with circular 

 disks. Flowers $ $, arranged in catkins or 

 h.eads, surrounded by opposite decussating 

 Fig. CLX1I. scales which are connate at the base, or altogether 



consolidated into a horizontal ring. $ Calyx 

 1 -leaved, transversely slit at the end, projecting from its bottom a monadelphous fila- 

 ment bearing 1-celled anthers, bursting longitudinally and centrally, so as to form a 

 pore. Pollen (in Gnetum, simple, smooth, oblong, Griffith), in Ephedra ellipsoid, with 

 6 longitudinal furrows. $ altogether naked, or sheltered by a false calyx consisting 

 of two scales, more or less combined, each of which surrounds one or two flowers. 

 Ovary 0. Ovule pointed by a style-like process formed from a third membrane sur- 

 rounding the nucleus. Seed drupaceous, before maturity pierced at the point and ter- 

 minated by a style-shaped protruded process ; finally pointless. Seed-coat thickish, 

 either altogether leathery, or shelly, or fibrous internally, and succulent externally ; in 

 Gnetum lined by acicular woody tissue. Embryo dicotyledonous, in the middle of 

 fleshy albumen ; radicle superior. 



Conifers and Cycads present features so peculiar that their separation from all other 

 Orders is a point concerning which there can be no difference of opinion. It is indeed 

 difficult to trace a plain transition from them to the other parts of the Vegetable 

 Kingdom in which perfect sexes are present. There exist, however, a few plants, not 

 very similar to each other in appearance, bearing the names Gnetum and Ephedra, in 

 which we find precisely the structure and habit that would be wished for by a theorist 

 searching for evidence to bring Gymnogens into communication with true Exogens ; 

 for one of them has all the appearance of a Chloranth, and the other of a Casuarina ; 

 and yet both retain the true peculiarities of Gymnogens. These are called Gnetacese, 

 and may in English be termed Joint Firs, for they are closely allied to Conifers, but are 

 distinctly known by their stems being jointed at every node. In these plants there is 

 little tendency to form cones, and in the genus Gnetum the development of the ovule is 

 so peculiar that botanists at one time, myself included, supposed that the real ovule 

 was in truth an ovary pierced at the summit, for it consists of an exterior shell of 

 considerable thickness and of a green colour ; within which is a thinner envelope through 

 which passes a tubular projection fringed at the point, and within these lies a nucleus, 

 as is represented in the accompanying figure of the young ovule of Gnetum Brunonia- 

 num, copied from an unpublished drawing by Mr. Griffith. So that this sort of ovule 

 has 3 distinct integuments, clear of the nucleus. It is to Mr. Griffith that I owe the 

 knowledge of the true nature of these plants. In a most elaborate unpublished Memoir 



Fig. CLXII. — Gnetum Gnemon : 1. a section of an ovule showing the three membranes, of which the 

 innermost protrudes in the form of a stigma. 



Fig CLXIII. — A thin section of the wood of Gnetum Gnemon, highly magnified, after A. Kiongniart 



