362 SYSTEMATIC BOTANY. 



Distribution. A small group, the members of which inhabit temperate 

 regions generally, or mountains in the tropics. 



Qualities and Uses. Agreeing in general with Pinaoeae j Podocarpw, 

 Dacrydium, Taxus (Yew), &c. yield valuable timber. The leaves of the 

 Yew are poisonous ; but the pulp of the berries does not appear to share 

 this property. The fruits of Salisburia adiantifolia are resinous and 

 astringent. 



GNETACE^E are small trees or shrubs, usually with jointed stems, 

 opposite, simple net- or parallel-ribbed, or minute and scale-like leaves, 

 and unisexual (rarely hermaphrodite) iiowers in catkins or heads ; anthers 

 2-3-celled, opening by pores ; female flower naked, or with two more or 

 less combined scales, surrounding 1 or 2 naked ovules (?) ; seed succulent; 

 embryo with two cotyledons, in the axis of fleshy perisperm. Illustrative 

 Genera : Ephreda, L. j Gnetum, L. ; Welwitschia, Hook. f. 



Affinities, &c. This Order is chiefly interesting as furnishing a link to 

 connect the Conifers with the Dicotyledons, if the plants be considered to 

 have a truly Gymnospermous organization of the flower (a view strongly 

 contested by Strasburger and others), while in general structure Ephedra 

 approaches to Casuarina, and Gnetum to Chloranthus. They are destitute 

 of the resin so characteristic of Conifers. The ovule presents the curious 

 peculiarity that a third integument, immediately investing the nucleus, 

 grows out into a long process like a style, and which projects from the 

 foramen of the outer coat. Welwitschia mirabilis (fig. 448), a native of 

 desert regions in South-western Tropical Africa, where it was discovered 

 by the botanist whose name it bears, is, in many respects, the most interest- 

 ing flowering plant now in existence. It consists of a woody trunk, about 

 2 feet high, with a long woody root, and terminating above in an irre- 

 gularly lobed saddle-like mass, 4-5 feet in diameter. From a groove 

 beneath the edge of this is given off, on each side, a broad leathery leaf, 

 some 6 feet long, and split into numerous thongs. These leaves are 

 supposed to be the persistent cotyledons ; and no others are produced, 

 though the plant attains an age of at least a hundred years, and probably 

 more. The disk at the top of the stem is marked by concentric lines. 

 The inflorescence consists of cones borne on forked branches which origi- 

 nate from the edge of the disk (fig. 449). The cones contain, some female 

 flowers, others male flowers ; the latter with an abortive ovule occupying 

 the extremity of the axis (fig. 450). The male flower consists of a perianth, 

 as in the male flowers of Ephedra, enclosing six stamens, united by their 

 filaments into a short tube, and bearing globose anthers, which open by a 

 3-rayed chink. In the centre of the flower is a body like an ovary, with 

 a terminal style-like prolongation and an expanded stigma. This pistil- 

 like structure invests the nucleus of the ovule, which, in this case, is desti- 

 tute of embryo-sac and embryo. The ovary-like body in this flower is 

 shown, from its mode of development and structure, to be homologous with 

 the coat of an ovule, and not to possess the characteristics of an ovary, except 

 so far as superficial resemblance is concerned. The long sty li form process 

 is similar to that which occurs in the ovule of Ephedra. The ovule, then, 

 of Welwitschia, according to Hooker, is strictly Gymnospermous, h'ke those 

 of Coniferse. Strasburger and McNab, however, dissent from this view. 



