150 ZANTHOXYLACEiE. 



length) : cotyledons oval-oblong, plane : radicle short, su- 

 perior. 



Shrubs, or small trees, unarmed; with alternate or some- 

 times opposite trifoliolate, or rarely pinnately quinquefoliolate 

 leaves, without stipules ; the leaflets ovate or oblong, entire 

 or serrulate, punctate with pellucid dots. Flowers small, 

 greenish-white, in terminal cymes or compound corymbs. 

 (Pistil sometimes tricarpellary and three-winged.) 



Etymology. HreXia, an ancient name of the Elm-tree, transferred to this 

 genus on account of the winged key-fruit, which resembles that of the Elm. 



Geographical Distribution. This genus consists of one species in- 

 digenous to the Middle, Southern, and Western United States, and one in 

 Florida, and two or three others in New Mexico and Mexico. 



Properties. The bark and foliage is bitter and strong-scented, and is 

 reputed to be anthelmintic. The fruit is said to be used as a substitute for 

 hops. 



PLATE 157. Ptelea trifoliata, Linn.; — a flowering branch of the 

 natural size. 



1 . Diagram of a tetramerous flower. 



2. A tetramerous sterile flower, enlarged. ^ 



3. Vertical section of the same. 



4. A stamen more magnified, seen from the outside. 



5. The same, seen from the inner side. 



''- 6. A pentamerous fertile flower, enlarged. 



7. A fertilized pistil, magnified, the ovary transversely divided. 



8. Vertical section of the same. 



9. An ovule, more magnified. 



10. A fruit, of the natural size. 



11. A magnified seed, from the right-hand cell, in its natural position. 



12. Vertical section of the same, showing a small, probably not fully 



grown embryo at the apex of the albumen. 



13. This embryo detached and more magnified (inverted).* 



* The seeds examined appeared to be mature ; but the embryo was probably 

 arrested in its development. Adr. de Jussieu has represented it, as described 

 above, with large and flat cotyledons, occupying nearly the whole length of the 

 albinnen. 



