1960] 



ANATOMY OF GUAYAXA XYRIDACEAE 



77 



the stem, bundles are embedded in thin- walled parenchyma. Each bundle m this 

 region is completely ensheathed by lignified cells like those of the sclerenchyma 

 cylinder. Leaf traces are uncommon in the cortical region (on account of the 

 long internodes), but where these are present, each bears a sclerenchyma cap on 

 the xylem face of the bundle. There are occasionally a few thick-walled lignified 

 parenchyma cells in the cortical region. 



Discussion. 



Despite the fact that the meager literature on stem anatomy does not suggest 

 the usefulness of this organ for systematic purposes, excellent generic and 

 specific characteristics are seemingly present, as outlined above. The smaller- 

 stemmed species of Abolboda are distinctive in their lack of central bundles, 

 their sclerenchyma cylinder, and their spongier, starch-free parenchyma, as 

 compared to the larger-stemmed species. The two species of Orectanthe are like 

 the larger-stemmed species of Abolboda in bundle distribution, but show a promi- 

 nent lignification of parenchyma ; this lignified core is clearly delimited from a 

 thin-walled cortical region. The rhizomatous stem of AchlyphiJa is distinctive 

 in Xyridaceae, but is not extremely unlike stems of Abolboda in its construc- 

 tion. Features of generic value include its prominent sclerification, distribution 

 of bundles, and development of an endodermis. 



Vessels. 



Longitudinal sections of stems in all the taxa named above were prepared, 

 and- these were used to demonstrate that in all taxa named, vessel elements with 

 simple perforation plates occur. Cheadle (1942) has indicated such vessel ele- 

 ments for two species of Xyris. 



LEAF 



The same groupings used for descriptions of stem anatomy may be used here. 

 The species and species-groups prove highly diversified, so that few generaliza- 

 tions can be offered. 



Smaller-stemmed Abolbodas. 



Species in this group are distinctive in their smaller leaf size, the relative 

 lack, or restriction of, photosynthetic tissue, and the presence of longitudinally- 

 oriented pockets of parenchyma which collapses at maturity and appears to have 

 been composed, in some instances at least, of chlorenchyma cells. Hypodermis 

 is absent, or present only in the more apical portions of the leaf. Stomata are 

 restricted to the lower surface. 



1. A. acaulis (figs. 31, 35). The basal portion of a leaf (fig. 31) consists of 

 parenchyma, isodiametric as seen in transectional outline, in which 4-5 veins 

 are embedded. Between the veins, zones of collapsed parenchyma are present. 

 Sclerenchyma completely ensheaths the veins; such sheaths are usually two 

 cells in thickness. At a higher level (fig. 36) a hypodermis begins to be differen- 

 tiated; it is prominent (by virtue of contrast with chlorenchyma) only in the 

 most apical portions of the leaf, where it consists of gelatinous-walled sclereids, 



Fig. 27. A. ciliata. Fig. 28. A. macrostacliya var. robustior. Fig. 29. Orectanthe ptarite- 

 puiana. Fig. 30. 0. sceptrum subsp. occidentalis. Scale = 0.5 mm, in 0.1 mm divisions. 



