92 BRITISH EOCENE FLORA. 



Order-GNETACEJE. 



The Gnetacese form a very distinct order of Gymnosperms. Their fruit is ovate and 

 drupaceous, or compressed and membranaceous, and the flowers are arranged in catkins. 

 They are characterised by their stems being jointed at every node and their ligneous 

 tissue being marked by circular discs. The three known genera, Welwitschia, Ephedra, 

 and Gnetum, are very dissimilar in appearance. While retaining the peculiarities of 

 Gymnosperms they present a plain transition to true Exogens. 



Welwitschia is a most singular and abnormal plant inhabiting the arid regions of 

 South-west Africa, between the 14th and 23rd degrees of south latitude. 



Gnetum inhabits the tropics of Asia and America, except an African and a Fijian 

 species. There are about fifteen species known, most of which possess large ovate or 

 lanceolate, dark, coriaceous leaves, with simple margin and anastomosing secondary veins. 

 Although some Eocene leaves are not dissimilar, the inflorescence, the fruit, and stems 

 are so peculiar and apparently so easily preserved, that in their complete absence from all 

 known fossil-bearing rocks, we must for the present conclude that no Gnetum formed part 

 of the European Tertiary Flora. The Ephedra, however, were widely spread in at least 

 the European Eocenes. 



Genus — Ephedra, Linn. 



The flowers are unisexual, most often dioecious. The fruit is drupaceous, oblong, 

 indehiscent, succulent, with a hardened interior, and formed of two carpels with a single 

 seed in each. The branches are slender, nodose, and jointed, erect or pendulous, and the 

 leaves very small and scale-like. Some thirty species are known. They are erect or 

 scandent, apparently leafless shrubs, copiously branching and abounding on the sandy 

 sea-shores of Eastern Europe, North Africa, temperate and sub-tropical Asia, and 

 extra-tropical America, from Chili to California. They closely resemble Casuarina, but 

 a critical examination enables their stems to be distinguished. 



Their peculiar jointed and striated stems can be picked out in abundance from the 

 innumerable masses of pyritised twigs left by the tide at Sheppey. I have also met with a 

 fruit, apparently a thin oval shell of the size of a small nutmeg kernel, labelled " Gnetum," 

 but probably intended for Ephedra, in the Bovverbank Collection from Sheppey ; but it 

 is now in fragments, and I am unable to restore it. There is no doubt, however, that a 

 species of Ephedra similar to that now living on the shores of the Mediterranean formed 

 part of the Sheppey fossil Flora. 



I have also come across a stone perforated with twigs which have all the characters 

 of Ephedra, on the shore of Lough Neagh. 



Species have been described by Unger, from Sotzka ; by Heer, from Switzerland ; and 

 by Ettingshausen, from Haring. 



