470 PHARMACEUTICAL BOTANY 
contains the single species Welwitschia mirabilis, a low growing 
plant of arid regions in southwest Africa. The genus Gnetum 
contains about 15 species of woody climbers native to the tropics 
of both hemispheres. The principal features of the Gnetum 
family are, as follows: 
Stems either unbranched and tuberous (Welwitschia) or 
branched and shrubby (Epfedra) or often climbing (Gnetum) and 
st 
td 
Fic. 354.—Transverse section through the outer region of a representative 
portion of the stem of Ephedra sinica. 400. c, cuticle; ep, epidermis; h, hypo- 
dermal fibers; ch, chlorenchyma of cortex, the outer layers of which are palisade-like; 
J, mesocortical fibers; td, tracheids and tr, trachea of secondary xylem; st, stoma. 
possessing open-collateral fibrovascular bundles. Resin canals 
are absent while true vessels (tracheae) are present in the second- 
ary xylem (distinction from conifers). Tracheids also occur in 
the xylem. Internodes and nodes are conspicuous in Ephedra 
and Gnetum. Leaves usually small, often reduced to scale-like 
structures and arranged in opposite or verticillate fashion. 
Flowers nearly always dioecious and exhibiting a membranous 
perianth of 2- to 4-bracts. Perianth of male flowers surrounding 
2 to 8 stamens. Female flowers showing an erect ovule with 1 to 
