FURTHER STUDIES OF YUCCAS. 193 



it to baccata. The smooth leaves of the specimens I have 

 seen are, however, quite unlike the rough foliage of the 

 usual northern form of baccata, and the question of the dis- 

 tinctness of valida may still be kept open. I think it very 

 probable that it will be found in the heart of Mexico, where 

 several little-studied Yuccas of the baccata set occur, as 

 well as in its present range on the peninsula of Lower Cali- 

 fornia. Nothing is known of its pollination. 



Y. FILIFERA, Chab. Nothing is known of the pollina- 

 tion of this Mexican tree Yucca, except that herbarium 

 specimens of its fruit show the work of Pronuba larvae, 

 from which Professor Kiley infers that a large and interest- 

 ing species of moth peculiar to it will be discovered.* 



B. CLISTOYUCCA, with leathery or spongy indehiscent fruits . 



Y. BREVIFOLIA, Engelin. (PI. 6-9, 21)f . This, our largest 

 tree Yucca, is interesting from several points of view. 

 Seedlings possess decidedly glaucous flexible leaves, rather 

 similar to those of young WJiipplei. At first a fleshy 

 round-pointed caudex develops below ground, from which 

 long simple tough roots spread in all directions ; but 

 this original descending axis disappears with age, so that 

 the old tree has a flat or irregular basal disk, from which 

 the tough roots, now as thick as a lead pencil, run into the 

 soil for a long distance. As a rule each plant forms only a 

 single trunk, but occasionally laterals develop, generally as 

 a result of injury to the main stem. Until it is eight or 

 ten feet high, the trunk is unbranched, and covered 

 throughout with the very rough and rigid, mostly yellowish- 

 green leaves, the lower of which are reflexed. When of 

 about this size, it blooms for the first time (PL 6), after 



* I. c. 121; Proc. Biol. Soc. Washn., vii. 96; Insect Life, iv. 371. As 

 a further reference to this species should be given Fenzi: Boll. Soc. 

 Tosc. ortic. xiv. 1889, 278, with plate. 



f See an article by Shinn, on "The Land of the Tree Yuccas," in 

 American Agriculturist, 1891, 689. 



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