A SOUTHWESTERN PLANT GROUP. 799 



made the basis for the primary division of the genus into three 

 groups : the Singuliflorce, the Geminiflorce, and the Paniculatce. 

 In all cases the flower-scape rises from the apex of the main axis 

 of the plant ; all the vital energy of often many years' growth is 

 centered there, and the plant throws up its blossom-stalk as the su- 

 preme effort of its existence, and, when the fruit has ripened, dies 

 — a strange phenomenon, and almost without parallel in any other 

 so extensive group. In the Singuliflorce is the simplest type of in- 

 florescence. The flowers are loosely spiked, each one in the axil of 

 a bract. To this group belongs our one Northern agave, the little 

 Agave Virginica, which grows from Maryland and southern Indi- 

 ana southwest ward into Texas. The Geminiflorce have the flowers 

 borne in pairs, and densely spiked along the scape. Variations- 

 which show transition between both these simpler groups and the 

 third occur. The Paniculatce have the scape more or less branch- 

 ing, often in the fashion of a candelabrum, each branch terminat- 

 ing in a dense cluster of flowers. These are the typical agaves r 

 the crowning glory of the genus. The familiar Agave Americana 

 is a representative of the Paniculatce, and so also the plant shown 

 in the accompanying photograph (Fig. 7), A gave Salmiana, a 

 magnificent species that blossomed in the Missouri Botanical 

 Garden in the summer of 1892. A splendid agave that commemo- 

 rates the founder of the Missouri Garden is the Agave Shawii r 

 dedicated by Engelmann to Henry Shaw ; and in turn the labors 

 of Engelmann have been fitly honored in the dedication to him of 

 a most striking type that he once presented to the Missouri Gar- 

 den. It blossomed there in the summer of 1891, and when it had 

 been clearly proved a new species it was duly christened by Di- 

 rector Trelease Agave Engelmanni (Fig. 5). The structure of 

 the agave flower is extremely unique in several particulars, but 

 further detail can not be entered into. Almost every step taken 

 in the investigation of the genus gives additional emphasis to the- 

 first impression, that it is one of the master marvels of plant life. 



It remains to add some passing notes on the wonderfully beau- 

 tiful genus which the lily family contributes to our group, the 

 yuccas. A glorious floral offering to the arid Southwest high- 

 lands they certainly are, and scientifically their structure is in 

 many ways scarcely less remarkable than that of the cacti and 

 agaves. But the consideration of these points will be passed over 

 here in order to call up more particularly the phenomenon that 

 makes the yucca an astounding mystery to naturalist and philoso- 

 pher, the manner of its cross-fertilization. For the fact is, we have- 

 here an extensive genus entirely incapable, save under most rarely 

 extraordinary circumstances, of self-fertilization, and entirely de- 

 pendent on one moth that fertilizes the flowers in order to insure- 

 food supply for its larvae in the ripening seeds. The problem of 



