a6 TRANS. ST. LOUIS ACAD. SCIENCE. 



in depth. J The three outer segments are usually narrower and often 

 a little shorter, and more frequently tinged with green or red along 

 the midrib and tip ; the three inner ones are broader (except ap- 

 parently in T. Guatemalensis, where they are narrower), more 

 petaloid, of more delicate texture and color, and, in some species, 

 tipped with a small bunch of short white wool. They possess a 

 certain, usually not pleasant, fragrance. 



The size of the flower and even the shape of the segments is 

 extremely variable in some of the species ( T. baccata^ T. Tre- 

 culiana^ T. rupicola)^ and can scarcely be used for diagnostic 

 purposes. 



The six stamens, in two series, but of nearly equal length, are 

 adnate to the base of the perigon, and always shorter than this, 

 and mostly shorter than the pistil ; only in Hesperoyucca they 

 are longer than the latter. Straight in the bud, they are fre- 

 quently more or less recurved and even uncinate after maturity, 

 in some forms more, in others less, but I am not able to discover 

 a specific character in this change of form. 



The filaments are fleshy and club-shaped, and in the true Yuc- 

 cas covered, especially upwards, with transparent one-celled 

 papillae or papillose hair ; a minute point on the obtuse, some- 

 times slightly trilobed apex bears the introrse anther. In Hespero- 

 yucca the filament is smooth, thicker upwards, but with an acute 

 tip. 



The anthers are comparatively small, 2I or usually 3-4 millim. 

 long ; in exceptional cases, only in cultivated plants of T. an- 

 ^ustifolia^ I have seen them 5-6 mm. long ; they are sagittate or 

 cordate at the base, rounded and entire or notched at tip, ad- 

 nate on the back and two-celled ; they open longitudinally just 

 before the perigon expands, and contracting to one-third or less 

 of their size, and curling backwards, expel the large, compa- 

 ratively scarce, globose, glutinous pollen grains of 0.055-0.070 

 mm. diameter. The size and shape of the anthers seem to me 

 to vary in the same species. 



Hesperoyucca has smaller, deeply cordate, emarginate, some- 

 what didymous anthers, \\-2 mm. long, and broader than long, 

 bearing pollen similar to that of the other Yuccas. 



The pistil in the true Yuccas is a cylindric or rather prismatic, 



X It is this day-time appearance which is almost always described and figxired, and which 

 S^ves an erroneous impression as to the form of the well developed flower. 



