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MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



[VOL. 10 



there are exceptional species within a genus; (2) reference to particular con- 

 ditions in lengthy anatomical terms, or with the aid of illustrations is necessary ; 

 and (3) some relatively subtle characteristics cannot be summarized in this man- 

 ner. The most important anatomical lines of evidence are cited below, and the 

 reader is referred to the foregoing descriptions, particularly to the "discussion" 

 section terminating each of the major portions above. 



Specific Characteristics. 



1. Abolboda. Characteristics of leaf anatomy and stem anatomy suggested 

 recognition of two species-groups, termed here "smaller-stemmed" abolbodas 

 and "larger-stemmed" abolbodas. Recognition of these as subgenera would 

 probably be premature. Within each of these groupings, leaf and stem anatomy 

 suggest specific characteristics also. Characteristics other than these do not 

 emphasize the two species-groups as much as they suggest characteristics of 

 individual species. The large stele of roots defines A. macrostachya, but genuine- 

 ly remarkable specific characteristics are offered hy the peculiar patterns of 

 endodermis-cell thickening. In the inflorescence axis, thickness of sclerenchyma 

 ring, presence of fibrous sheaths on pith bundles, and sclerification of epidermal 

 cells offer a number of characteristics. Distinctive patterns in number of bundles, 

 size, sclerenchyma and chlorenchyma presence and distribution offer further 

 characteristics in sepals, and, to a lesser extent, in bracts. Perhaps the best 

 specific characteristics are evident in pollen in such respects as shape and size of 

 spines, nexine thickness, and diameter. 



2. Orectanthe. Anatomical features by which 0. ptaritepuiana may be 

 differentiated from 0. sceptrum include relative lignification of the central 

 portion of the stem ; thickness, epidermal sclerification and shape of bundles in 

 leaves; distribution of parenchyma in the sepals; size and sexine ornamentation 

 of pollen grains. 



Generic Differences. 



The closest relationships among genera of Xyridaceae is that between Ahol- 

 boda and Orectanthe. Segregation of the latter genus is well deserved, however. 

 Orectantlie has larger stems with a distribution of sclerenchyma different from 

 that in Abrtboda. Orectanthe has more bundles in its leaves, more bundle-sheath 

 extensions, a tendency towards abaxial hypodermis production, and no thorn- 

 like leaf-tip with peculiar tracheids. It has spongy chlorenchyma and lignified 

 bundle sheaths in the cortex of the inflorescence axis. It has distinctive sepal 

 size and anatomy, and the inflorescence-axis bract is notably lacking in scleren- 

 chyma or other differentiation. Orectanthe lacks staminodia, has more elaborate 

 corolla venation, and a massive anther connective. Capsule-valve anatomy and 

 especially seed anatomy provide excellent characteristics to distinguish the two 

 genera. Pollen morphology provides an exemplary instance of a generic degree 

 of distinction between Abolboda and Orectanthe. 



Achlyphila could probably be defined, on the basis of present knowledge, on 

 a number of anatomical features. The root offers peculiar endodermis characters 

 and vessels well toward the interior of the core, which, however, lacks central 

 vessels. The stem shows modifications corresponding with its rhizomatous habit, 

 such as a stem endodermis. The leaves have a peculiar equitant habit, and the 



