ONETACE^. 415 



The most remarkable member of the order is WelwitscJda mirabilis 

 (Fig. 302) discovered by Dr. Welwitsch in 1860, and described by Dr. 

 Hooker in 1862.* It consists of a short, thick, woody stem rising 

 30 cm. (1 ft.) above the ground, and having a diameter of from 30 to 

 50 cm. (12 to 20 in.), and even attaining in some cases, according to the 

 discoverer, a diameter of 1.4 metres (4 It.). From the lower portion 

 of this stem a stout tap-root passes downward, branching more or less 

 at its lower end. The top of the stem is nearly flat, there being usu- 

 ally a slight depression across its diameter. There are only two leaves 

 attached to this curious stem, and from the study of the young plants 

 it seems probable that they are the persistent cotyledons. They arise 

 in two deep grooves in the circumference of the upper part of the stem, 

 and as they continue to grow at their bases they eventually attain a 

 great length, being nearly two metres long (6 ft.) in full grown plants. 

 They are thick and leathery in texture, and their fibre-vascular bun- 

 dles are all parallel and free from each other, running from the base of 

 the leaf to its split and frayed apex. From the circumference of the 

 stem, above and close to the bates of the leaves, spring stout branching 

 peduncles, which bear clusters of s.carlet cones (Figs. 302 and 303). 

 These cones are composed of numerous opposite bracts arranged in 

 four rows. In the axil of each bract there is a single flower, consist- 

 ing in the male cones of a perianth of two pairs of decussating bracts 

 enclosing a ring of partly united stamens ; within these is a rudimen- 

 tary, abortive ovule, whose sinjrle coat is curiously prolonged so as to 

 resemble a pistil with style and expanded stigma. In the flowers of 

 the female cones the perianth is a compressed, winged tube, lying 

 within the broad scales. There are no rudiments of stamens ; and in 

 the centre of the perianth there is placed a single erect ovule with one 

 elongated integument. 



It will thus be seen that the cones of WelwitscJda, while bearing 

 some external resemblance to those of Coniferse, are not homologous 

 with them ; in Welwitschia they are short, flower-bearing, bracted axes ; 

 in Coniferse they are stamen-bearing or pistil-bearing axes, in other 

 words, each cone is a multistaminate or multiovulate flower. 



Fossil Gymnosperms. Gymnosperms first appeared in the Devo- 

 nian, in which they were represented by species of Prototaxis, Cladoxy- 

 lon and Scldzoxylon, doubtfully referred by Schimperf to the Coniferse. 

 True conifers were present in the Carboniferous, in the Permian they 

 were abundant, and in the Tertiary exceedingly so. Araucaria was 

 represented in the Jurassic by several species. Pinus, Abies, Cedrus 

 and Sequoia originated during the Cretaceous period, and were repre- 



* " On Welwitschia, a new Genus of Gnetaceae," by J. D. Hooker, 

 in "Transactions of the Linnean Society," Vol. XXIV. 



f " Traite de Paleontologie Vegetale," par W. Ph. Schimper, Paris, 

 1869-1874. 



