340 FOURTH GROUP. SEED-PLANTS. 



C. GNETACEAE 1 . 



This division includes three genera of strikingly different habit. The Ephedrae 

 are shrubs which have no large foliage-leaves, but long slender cylindrical branches 

 with a green rind which bear two opposite minute leaves at their joints ; these leaves 

 cohere and form a bidentate sheath, and lateral branches grow from their axils. In 

 Gnetum the leaves are also opposite to one another on the jointed axis, but they are 

 large and stalked, with a broadly lanceolate lamina and pinnate venation. Finally, 

 Welwitschia miralilis, a very remarkable plant in other respects also, has only two 

 foliage leaves of enormous size, which are placed crosswise with respect to the deci- 

 duous cotyledons, and when old are split up and lie stretched out on the ground. The 

 stem is always short, rising only a little way above the ground, is broad above with a 

 furrow over the apex, and swells out below where it passes into the tap-root 2 . 



The flowers of the Gnetaceae are unisexual in dioecious (Ephedra) or monoecious 

 inflorescences ; these inflorescences have a clearly denned form and spring in Ephedra 

 and Gnetum from the axils of the opposite leaves. The male flower of these genera 

 consists of a small bipartite perianth with a central stalk-like filament, which in Gnetum 

 is bifid above and bears two bilocular anthers, and in Ephedra has a larger number 

 of anthers crowded together into a small head. The female flower also, according to 

 Eichler 3 , has a perianth 4 which is flask-shaped in Gnetum and in three divisions in 

 Ephedra, and encloses a centrally placed ovule which has one integument in Ephedra 

 and two in Gnetum, the inner one being prolonged like a style. A small cell is 

 separated off in the pollen-grain of Ephedra as in that of the Cupressineae ; the 

 prothallium of the macrospore (the embryo-sac) produces from three to five arche- 

 gonia with an elongated central cell, and a very long neck divided by transverse 

 walls and with a ventral canal-cell distinctly visible at its base (Strasburger). In 

 Gnetum the inflorescence which springs from the axil of a foliage-leaf consists of a 

 jointed axis with verticillate leaves, in the axils of which the male and female 

 flowers are crowded together. But the female flowers in the apparently hermaphrodite 

 inflorescences are not capable of development, and are distinguished from the fertile 

 flowers of the female inflorescences by having two only instead of three envelopes, 

 the middle one being abortive. The inflorescences of Welwitschia mirabilis are 

 dichotomously branched cymes nearly a foot high ; they spring from the circum- 

 ference of the broad apex of the stem above the insertion of the huge leaves. The 

 round and jointed branches of the inflorescence proceed from the axils of the bracts, 

 and bear rather long erect cylindrical cones ; the tones are covered with from seventy 

 to ninety broadly ovate scale-leaves standing in four rows closely one above another, 

 in the axils of which are the single flowers, male and female being distributed on 

 different cones. The male flowers are pseudo-hermaphrodite and have a perianth of 



1 Strasburger, as quoted under the Coniferae. 



2 For further information on this strange plant, see Flora, 1863, p. 459, and Bower, On Wel- 

 witschia (Q. J. M. S. 1881). 



3 Flora, 1863, pp. 463, 531. 



4 This is considered by Strasburger to be a simple outer integument, and so Ephedra would 

 have two and Gnetum three integuments. How we name these envelopes appears to me to be 

 unimportant, but the analogy of the other forms is in favour of the designation given by Strasburger. 



