252 PEOCEEDINGS OF THE AMERICAN ACADEMY 



3. Y. canaliculata, Hook. Caudex 6 to 25 feet high, branching 

 at top : leaves very long (2 \ to 4| feet by 2 or 3 inches wide), straight 

 and very rigid, deeply channelled, rough on the back : panicle subses- 

 sile, ovate, 2 to 4 feet long, densely flowered, nearly glabrous, with 

 large ovate or broadly lanceolate bracts : flowers cream-white ; seg- 

 ments ovate or ovate-lanceolate, acute or acuminate, \\ to 2\ inches 

 long : filaments scarcely papillose, nearly equalling the pistil : style 

 slender ; stigmas narrow, deeply 2-lobed : fruit subcylindric, strongly 

 beaked, 3 or 4 inches long: seeds 3 to 3£ lines broad. — Bot. Mag. 

 t. 5201. T. Treculiana, Carr. Rev. Hort. 7. 280 (name only); Engelm. 

 1. c. 41. T. longifolia, Engelm. ; Buckley, Proc. Philad. Acad. 1862, 8. 

 Texas to Northern Mexico. 



*+++++ Leaves coarsely filaraentose on the margin. 



4. Y. baccata, Torr. Caudex short or none : leaves very thick and 

 rigid, 1^ to 3 feet long by an inch or two wide, channelled or concave, 

 rough especially on the back, tipped by a very stout brown spine : 

 panicle pedunculate, usually glabrous, with ovate-lanceolate or ovate 

 bracts : perianth-segments narrow, 2£ to 3 inches long : stamens 

 equalling the ovary: .^tyle more or less elongated, slender: fruit 

 oval or cylindric, 3 to 5 inches long, dark purple, often long-beaked : 

 seeds 4 to 8 lines broad, a line thick or more. — Bot. Mex. Bound. 

 221 : Engelm. 1. c. 44: 111. Hort. 3 ser. t. 115. S. Colorado and W. 

 Texas to S. California and Northern Mexico. 



Var. australis, Engelm. 1. c. Caudex taller (often 10 to 50 feet), 

 branching : leaves thinner and smoother, with finer fibres : flowers 

 smaller (H inches long), with ovate segments and short style. — The 

 more southern Mexican form. 



5. Y. Schottii, Engelm. 1. c. 46. Caudex 2 to 5 feet high, branched 

 from the base : leaves straight, rigid, about 9 inches long by 6 or 8 

 lines wide, concave, somewhat pungent, smooth, with very slender 

 straight marginal threads : panicle loosely flowered, with flexuous 

 peduncle and branches, and large lanceolate bracts : flowers rather 

 small : style and stigmas short : fruit ovate, 2 inches long, shortly 

 beaked. — S. Arizona. 



-t- h- Fruit becoming dry and spongy, indehiscent, erect : seeds thickish, smooth 

 and scarcely margined, with entire albumen. Tall and branching, with 

 sessile panicles and serrulate leaves. 



6. Y. brevifolia, Engelm. Caudex 15 to 30 feet high : leaves 

 3 to 8 inches long by as many lines wide, very rough and rigid, atten- 

 uate to a stout spine, nearly flat above : panicle pyramidal, with white 



