114 ZYGOPHYLLACEiE. 



scales attached to the base of the filaments on the inner side, in several gen- 

 era, are undoubtedly a deduplication of the stamens. 



This family consists of about fifteen known genera, no one of which is nu- 

 merous in species. The greater part belong to the warmer portion of the 

 northern temperate zone, where they are more abundant in the Old World 

 than in the New. The remainder are tropical, with a few at the Cape of 

 Good Hope, one genus in New Holland, and two or three in Chili and Pa- 

 raguay. Guaiacum, which comprises all the trees of the order, belongs to 

 America, near the tropic of Cancer. 



The wood, bark, &c., of all Zygophyllaceous plants contain an acrid and 

 bitter, more or less resinous principle, and the herbage usually exhales an 

 ungrateful odor. That of Zygophyllum Fabago is sometimes employed as a 

 vermifuge, and its flower-buds as a substitute for capers. The ligneous 

 plants of the order are remarkable for the extreme hardness of their wood. 

 That of one or more species of Guaiacum furnishes the Lignum Vitce. of 

 commerce, the hardest and heaviest wood known, and which never splits, 

 owing to the diagonal crossing of the successive layers, in the same way as 

 in our Nyssa. From this wood is obtained the guaiacum of the shops, a res- 

 inous, acrid-bitter substance, partly soluble in water, so well known in med- 

 icine as an alterative, &c. 



Conspectus of the United States Genera. 



Tribe I. TRIBULE^E. — Seeds destitute of albumen. 



Tribulus. (Plate 145.) Calyx deciduous. Fruit of five transversely plu- 

 rilocellate few-seeded cocci, leaving no central axis when they sep- 

 arate. 



Kallstromia. (Plate 146.) Calyx persistent. Fruit of ten one-seeded 

 cocci which separate at maturity from a prolonged central axis. 



Tribe H. ZYGOPHYLLE.^. — Seeds with a hard albumen. 



Larrea. (Plate 147.) Filaments appendaged by a two-cleft scale. Fruit 

 separating into five indcbiscent cocci. Seed with a membranaceous 

 testa. Cotyledons narrow, parallel with the axis. 



Guaiacum. (Plate 148.) Filaments naked. Fruit rather fleshy, 2- 5- 

 lobed, the angles acute or wing-like. Testa fleshy, separable. Coty- 

 ledons broad, contrary to the axis. 



Guaiacidum. (Subgen., Plate 149.) Filaments appendiculate with a 

 small scale : otherwise as in Guaiacum. 



