THE SPERMATOPHYTES - 469 
OrpDER GNETALES 
The Gnetales comprise the single family, Gnetacea, which has 
three genera which in certain respects show a closer resemblance 
to the angiosperms than do other gymnosperms. 
Fic. 353.—Cross section of a lower internode of the green stem of Ephedra sinica, 
a source of the drug Mahuang. 17, ridge; note many of the ridges are papillated; 
c, cuticle of epidermis; co, cortex; mf, mesocortical fibers; Af, hypodermal fibers; x, 
xylem of an older (primary) bundle which has undergone secondary thickening; 
Pp; pericyclic fibers just beneath which is phloem, ca, cambium; sx, secondary xylem; 
px, end of protoxylem; ph, phloem of a secondary bundle; /d, tracheids with bordered 
pits; ér, trachea; m, pith. Note the narrow medullary rays separating the open 
collateral bundles. 
Family Gnetacea. The Gnetum family includes the genera 
Ephedra, Welwitschia and Gnetum, each genus representing a differ- 
ent type of plant. The Ephedras include about 30 species of 
straggling shrubs or low bushy plants of warm dry regions of the 
northern hemisphere, a number of species of which are used 
medicinally because of their ephedrine content. Welwitschia 
