SPERMATOPHYTES 



229 



jted throughout the tropics of both hemispheres. Gnetales have always 

 attracted attention from the fact that in certain characters they resemble 

 angiosperms more nearly than do the other gymnosperms. 



FlG. 517. — Tumboa, showing the heavy conical body and the two-lobed crown bear- 

 ing two broad parallel-veined leaves (in the photograph split into shreds) and strobilus- 

 bearing branches. 



Sporophyte. — The species of Ephedra are straggling shrubs, with 

 long-jointed and fluted green stems, and scalelike opposite leaves form- 

 ing at each joint a two-toothed sheath 

 (figs. 511, 512, 975). Tumboa has a 

 huge, woody, turnip-shaped body, 

 whose crown bears a single pair of 

 elongated , strap-shaped, parallel- veined, 

 and persistent leaves (fig. 517). The 

 species of Gnetum are small trees or 

 woody twiners with leathery, net- 

 veined, opposite leaves, resembling 

 those of dicotyledons (fig. 522). It 

 will be observed that a constant char- 

 acter of the group is the cyclic (op- 

 posite) leaves, a feature found among 

 Coniferales only in the Cupressineae. 



Vascular anatomy. — It is in their 

 vascular anatomy that the Gnetales 



show a striking angiospcrm character. The secondary wood dots not 

 consist exclusively of tracheids with bordered pits, as in the other gym- 



Figs. 518, 519. — Ovulate (5 1 8) and 

 staminate (519) strobili of Tumboa. 

 — 518, after Le Maiout and De- 

 caisne; 519, after Hooker. 



