GYMNOSPERM^. 



141 



Order.— GNETACE^. 



The third order of Gymnosperrase, though comprising but three genera, is of the 

 highest possible interest, for it possesses characters which serve in some respects to bridge 

 the immense gap separating the Conifera? from the angiospermous Dicotyledons. The 

 three genera, Ej)hedra, Gnettim, WelwitscJna, differ as much as even the various tribes in 

 the Coniferae from each other, and it is obvious that there can be no very close 

 relationship between them, though sufficient likeness exists to allow them to be grouped 

 in a single order. Saporta and Marion regard them as so many offshoots which have 

 fallen out at widely different periods on the line of march, and remained stationary, — in 

 other words, whose development has been arrested whilst their companions have pro- 

 gressed towards Angiosperms. At the same time, they believe them to be descended 

 from a common ancestor of the Taxea, rather than that they are direct links between 

 the existing Conifera and Angiosperms. Their origin must, in any case, be very 

 remote, notwithstanding that so few traces of them have been discovered. Striated and 

 articulated branches and scales have been described by Heer as Ejjhedriies, from the 

 Jurassic of Siberia, and Saporta refers to analogous remains from the Inferior Oolite of 

 the Cote d'Or. A more important discovery, however, is that of the female organ of an 

 Ephedra-like plant in the Upper Carboniferous of the district of Autun, recently described 

 by Renault in the ' Comptes Rendus ' of the Erencli Academy. 



All the genera have their organs arranged in pairs, on a decussate plan, each alternate 

 pair being at right angles to the last. Their embryos are dicotyledonous and stems 

 jointed. Their wood has the usual Gymnospermous structure, and is marked with discs 

 resembling especially that of Fhyllocladus, though approaching in its greater complexity 

 to that of Dicotyledons. 



Ephreda seems by far the most primitive of the genera. Its species are all shrubs, 

 without foliage leaves, and with green-jointed and repeatedly branching stems. A pair of 

 opposite, minute, and partly sheathing leaves occur at each node, and the branches as 

 well as the flowers proceed from their axils. The flowers are arranged in dioecious inflores- 

 cences, the male in catkins, and the female terminal on axillary stalks. 



The former possess an involucre formed by a pair of bracts, partly soldered together, from 

 the middle of which rises a staminal column bearing a number of anthers, or pollen 

 chambers, corresponding to microspores and stamens. The pollen grains are divided 

 across internally, according to Strasburger, by a membrane, as in the Abietinea, only 

 thinner. The female organs are protected by an integument of altered leaves, which form a 

 rudimentary ovary. The ovule corresponds to that of the Taxea, and the endosperm 

 produces but one archegonium. The fruit is a succulent cone, formed of two carpels, 

 with a single seed in each. 



