726 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM. 



terminal on a little shoot of its own. The seeds in this group are frequently 

 embedded in a fleshy investment (often arillar in nature). Besides the Yews, there 

 are included several peculiar Australasian forms, and the Maidenhair Tree, Gingko 

 biloba {cf. fig. 337 ^ p. 443). There are about 70 species of TaxacesB. 



Class III.— GNETALES. 

 Alliance XXVIIL 

 Family : Gnetaceoe. 



This family which includes three very dissimilar genera. Ephedra, Gnetura, and 

 Welwitschia, is by no means easy to define. In habit they are all of them quite 

 unlike the members of the two preceding classes, but yet they fall under the sub- 

 phylum Gymnospermse in view of the fact that the pollen-grain has direct access 

 to the nucellus of the ovule and from the resemblance (rather remote) which their 

 ovules and embryogeny presents to other Gymnosperms. Thej' agree amongst them- 

 selves in possessing flowers with perianths, vessels in their wood, and in the absence 

 of resin-ducts from their tissues. 



Ephedra is a good example of a switch-plant, having jointed assimilating shoots 

 with little scale-like leaves at the nodes, as in Casuarina or Equisetum. The 

 flowers which are borne in little clusters, are small and unisexual. The male flower 

 consists of a central columnar stamen bearing 2-8 anthers and inclosed in a 2-leaved 

 perianth. The female flower has an ovule with one integument and a little 

 perianth. As the seed ripens the bracts around the flower become red and fleshy. 

 There are some 20 species scattered over the warmer regions of the globe, including 

 the Himalayas, Mediterranean, and Mexico. 



Gnetum occurs as a liane or erect tree, and has expanded leaves like a Dicoty- 

 ledon, in decussating pairs. The flowers occur in clustered, catkin-like spikes, on 

 M-hich they are arranged in whorls. The male flowers are very like those of 

 Ephedra, the female have a central ovule with 2 integuments inclosed in a flask- 

 shaped perianth. On ripening, the perianth becomes fleshy, and the outer integu- 

 ment of the ovule hardens to a stone. There are 15 species, distributed in the 

 tropics. 



Welwitschia mirabilis is a plant altogether unique. Discovered some thirty- 

 five years ago by the botanical explorer Welwitsch, it has foi-med the subjec^ of a 

 classical monograph by Hooker. It occurs in the desert regions of West Tropical 

 Africa (Angola, Damaraland, kc). The stem is dwarf and top-shaped {cf. fig. 411), 

 and may attain more than a metre in diameter. The summit of the plant never 

 reaches far above the surface, and it bears two huge leathery leaves which sprawl 

 on the sand on either hand. Actually 4 leaves are produced, the 2 cotyledons, 

 which fall away whilst the plant is still quite young, and an additional pair placed 

 at right angles to the cotyledons and peraisting throughout the life of the plant. 

 These 2 leaves grow continually at the base whilst their apical regions become 



