191 1.] TRELEASE— THE DESERT GROUP X0LIXE.5:. 407 



Biology. 



All Xoline?e are perennial, and, as would be expected from their 

 habitats, they are pronounced xerophytes with a rather succulent 

 caudex," either small and insignificant or moderately developed, and 

 then either prostrate or erect, or even of tree size (/>/. 1-4), and 

 rather hard usually rough-edged or even prickly leaves^'*^ covered by 

 a well-cuticularized epidermis, the stomata usually arranged in lines 

 overlying the parenchyma between strong fibrous bundles and 

 either furnished with an outer vestibule as in Agave, etc. (Dasyli- 

 rioii), or located between prominent ribs that, especially in NoUna, 

 are often covered with more or less interlocking papillae.^^-^*' They 

 occur most strikingly in suth desert associations- as count Agave, 

 Yucca and Hcchtia among their characteristic components {pi. 2,4). 

 In many species the tip of the leaf shreds into a sometimes brush- 

 like bunch of fibers, and in one (Nolina Bigelovii) the margin 

 breaks away sparingly — in kind, rather than quantity, recalling the 

 fibrous exfoliation characteristic of many yuccas and of one large 

 group of spicate agaves. From a study, of the leaf-tip of Dasylirion 

 acrotriche, Zuccarini-* was led to believe that what passes for the 

 leaf is really a petiole with ventral ligule, the blade, considered as 

 peltate, being represented by the more dorsal shreds only. The 

 prevalent dorsal insertion of the haustorium on the cotyledonary 

 sheath in seedlings of this group is worthy of note in connection 

 with this opinion (pi. ij). 



Though sometimes weakened or even destroyed by flowering 

 under cultivation, all of the Xolineae appear to be normally poly- 

 carpic. The terminal inflorescence^--* is essentially of one type 

 though varied from a thin lax raceme-like wand into a stout com- 

 pound spike with short and broad divisions or an open simple, com- 

 pound or even decompound panicle (pi. 5). Whatever its form, 

 the flowers are clustered, usually two or three together, in the axils 

 of small prevailingly denticulate bractlets, either on cushions so 

 short that they appear to come from the main axis, or, more com- 

 monly, on evident secondary or tertiary branches (pi. 6, 7). The 

 primary branches appear to be 8-ranked^' and the bracts are often 

 large and conspicuous, those which support the ultimate flower 

 clusters being scarcely larger than the bractlets. 



