GNETALES 



369 



nificance. In Gnetum, as in Ephedra, the secondary wood contains 

 true vessels associated with gymnospermous tracheids. 



The vascular anatomy of 

 the group needs a wider range 

 of investigation than has been 

 given to it, and this has been 

 partially supplied by a recent 

 investigation by Hill and 

 DeFradste (28). The traces 

 entering the base of each coty- 

 ledon are two in Ephedra, four 

 (in two pairs) in Welimtschia, 

 and four or five in Gnetum. 

 The strands of the hypocotyl 

 are inserted on the cotyle- 

 donary strands, and are four 

 in Ephedra, eight or less ih 

 Welwitschia (quickly reduced 

 to four), and a variable 

 number (about 12-15) ^^ 

 Gnetum. The transition to 

 root structure occurs in the 

 lower region of the hypocotyl, 

 and in all cases the primary 

 root is diarch. 



On the whole, the meager 

 data available suggest a group 



Figs. 410-412. — Welwitschia mirabilis: 

 spicular cells from the perianth of the stami- 

 nate flower; fig. 410, a branching cell, the 

 branching represented in one plane; fig. 411, 

 a simple cell; fig. 412, the cut end of a long 

 cell, with lumen almost closed and the sur- 

 face covered by crystals of calcium oxalate; 

 X22S. 



farther removed from ferns 



than other groups of gymnosperms, and one that has developed more 



or less completely the true vessels characteristic of angiosperms. 



THE LEAF 



The opposite leaves of Ephedra, reduced to a two-toothed and 

 scaly sheath, certainly suggest ancestors with true foliage leaves, 

 and occasionally such leaves are developed now. 



The single pair of long-lived parallel-veined leaves of Welwitschia 

 are remarkable. The stomata are in rows and deeply sunken, and 



