ENGELMANN — NOTES ON THE GENUS YUCCA. 25 



vary considerably, even in forms of the same species. The shape 

 of the leaf is quite variable, and more so still its color, its thick- 

 ness, its stiffness, (hence its direction) and the nature of its ter- 

 minal spine ; broader leaves, with abundant parenchyma are apt 

 to become plicate, while in the same species leaves of stronger 

 fibrous structure are even. The characters derived from the 

 roughness and the peculiar structure of the stomatic surroundings, 

 as above detailed, are also inconstant, and therefore unreliable. 



INFLORESCENCE. 



The inflorescence, which terminates the axis in Yucca, usually 

 consists of a compound raceme or panicle of different dimensions, 

 from two to three or four feet high, with differently developed 

 lateral branches, and, therefore, of different shape, oval, lanceo- 

 late or pyramidal, and in one species at least (the northern form 

 of T. angustifolia) reduced to a simple raceme or spike. This 

 inflorescence is nearly sessile between the uppermost leaves, 

 especially in the arborescent species ; or it is raised on a longer 

 or shorter scape, sometimes longer than the inflorescence itself, 

 principally in the acaulescent forms. The scape bears reduced, 

 bract-like leaves, those of the inflorescence itself usually becoming 

 quite small and membranaceous, or, in some southern species, in- 

 creasing in size, broad, concave and spathe-like, fleshy and dis- 

 colored. The inflorescence is smooth or rough or pubescent, but 

 no important value can be assigned to these differences. The 

 pedicels are single or (on reduced branchlets) clustered, always 

 distinct, but shorter than the flowers, curved, patulous, declined 

 or pendulous, never, during the flowering period, erect. 



FLOWERS. 



The Yucca flower consists of a perigon of six oval or lance- 

 oval segments, united at base with one another, with the stamens 

 and with the pistil, and not articulated, so that they wither after 

 flowering without falling off. The perigon, expanding only for 

 one evening and night, forms a shallow cup of whitish, cream- 

 white,t or greenish-white color, sometimes externally tinged 

 with purple, of two to five inches in diameter ; on the following 

 morning, the fading segments conniving, the flower assumes a 

 globose or deep bell shape, of one and one-fourth to three inches 



f The flowers of T. canaliculata are described and figured in the Botanical Magazine as 

 " straw-yellow." 



