366 



:morphology of gymnosperms 



leaves succeeds the cotyledons (fig. 455), and is the only pair of foliage 

 leaves produced, growing continuously at the base, where they are 

 protected by the groove. These leaves last through the lifetime of 

 the plant, which is said to reach more than one hundred years. 



Fig. 408. — Welwitschia mirabilis: in the foreground are two plants with lacerated 

 eaves; in the background are seven more plants. — From a photograph by H. Schenck. 



The species of Gnetum are either small trees or woody climbers, 

 being among the lianas of tropical forests (fig. 409) . The leaves are 

 leathery in texture, and are very suggestive of those of dicotyledons, 

 the well-developed opposite leaves being lanceolate to ovate in outline 

 and pinnately net-veined. 



VASCULAR ANATOMY 



So far as known, all traces of mesarch structure are lacking among 

 the Gnetales, although it is altogether probable that it may be found 

 in some peripheral members. However this may be, in this feature, 

 as well as in others, the Gnetales seem farther removed from the ferns 

 than any other group of gymnosperms, the only suggestion of con- 

 nection being the foliar gaps. 



In Ephedra there is a persistent primary cambium, but not much 



