1960] 



ANATOMY OF GUAYANA XYRIDACEAE 



91 



species characters are difficult to offer. The inflorescence stems of Abolboda 

 macrostachya are distinctive on account of their greater size (with more numer- 

 ous bundles). Special features in the axes of A. americana (a single circle of 

 "pith" bundles; collapsed parenchyma pockets) and A. ciliata (1-2 circles of 

 "pith" bundles; prominent protoxylem lacunae in these) may be noted. The 

 extent of sclerenchyma seems roughly correlated, in Abolboda, with size of 

 the axis, and the sclerenchyma ring in A. macrostachya is much wider than in 

 A. americana. Likewise, the very wide sclerenchyma cylinder in Orectanthe 

 may be correlated with the large diameter of that axis. The sclerified epidermis, 

 the lack of concentric arrangement of bundles, the presence of scattered 

 bundles in the cortical region, and the presence on these of fibrous sheaths are 

 all characters which differ to a certain extent from comparable conditions in 

 Abolboda, and enforce the generic status of Orectanthe. The descriptions of 

 Achlyphila above have shown that inflorescence-axis anatomy serves both to 

 distinguish this genus genetically, and to relate the genus to other Xyridaceae, 

 probably to Xyris most closely. 



Vessels. 



Solereder and Meyer (1929) cite a report of vessels with simple perforation 

 plates in inflorescence axes of Xyris caroliniana, X. indica, and X. lacera. 

 In the present study, such vessel elements were observed in longitudinal sec- 

 tions of inflorescence axes of the following taxa : Abolboda acicularis, A. ameri- 

 cana, A. macrostachya var. macrostachya, A. macrostachya var. robusiior, and 

 Orectanthe sceptrum. Cheadle (1942) indicates vessels with simple perforation 

 plates in Xyris flesuosa and A', smalliana. 



INFLORESCENCE BRACTS 



One or more bracts tend to occur along the inflorescence axis, and several 

 are associated with the congested inflorescence itself. The former are here 

 termed inflorescence-axis bracts and the latter inflorescence bracts. These bracts 

 show patterns of structure different from those of sepals or leaves, and are 

 worthy of description. In some instances {Abolboda. acicularis, A. ciliata) the 

 difference between structure of inflorescence-axis bracts and sepals is not very 

 great. Because inflorescence-axis bracts and inflorescence bracts vary in structure 

 from base to apex, and even within a plant, depending on their position, their 

 structure is difficult to categorize accurately in all instances. Sections studied 

 are discussed by species. 



Abolboda. 



1. A. acaulis. Because of the subsessile nature of the inflorescence in this 

 species, bracts might best be regarded as inflorescence bracts. Such bracts have 

 three veins in a non-photosynthetic parenchyma. Sclerenchyma is absent. 



2. A. americana (fig. 24). An inflorescence bract is illustrated for this 

 species. Three veins are present. The middle one of these is embedded in a 

 sclerenchyma band which extends between the two surfaces. 



3. A. ciliata (fig. 17). The illustration represents the basal portion of an 

 inflorescence-axis bract. Numerous veins are present. These are encased in 

 sclerenchyma sheaths, some of which are continuous with the sclerified adaxial 

 surface. Chlorenchyma is present on the abaxial surface. 



