1960] 



ANATOMY OF GUAYANA XYRIDACEAE 



93 



sepals. The non-keeled sepals were found to have approximately the same 

 structure as the winged portion of a keeled sepal (compare, for example, figures 

 21 and 64), so that separate descriptions are not necessary. The chief variation 

 of significance is the relative distribution and presence of sclerenchyma and 

 (if present) chlorenchyma. To a large extent, the distribution of these tissues 

 in comparison with non-photosynthetic parenchyma cells provides distinctions 

 of taxonomic importance. The patterns are best summarized in terms of species. 



Abolboda. 



1. A. acaulis (fig. 56). The majority of the sepal is composed of lignified 

 parenchyma, in which the three bundles are embedded. Chlorenchyma occurs in 

 the keel of the sepal. 



2. .4. acieularis (fig. 57). The adaxial face of the sepal is composed of 

 thick-walled sclerenchyma ; the pattern of distribution parallels the outline of 

 the bract; the portion adaxial to the keel contains the single vascular bundle. 

 The outer face of the bract contains spherical chlorenchyma cells ; a small zone 

 of non-photosynthetic parenchyma is present in the keel. 



3. A. americana (fig. 58). The structure of this sepal is virtually the same 

 as that shown for A. acaulis. 



4. A. ciliata (fig. 59). The sepal of this species contains sclerenchyma, 

 which is present on the adaxial face and extends toward the keel, where it 

 encloses the midvein. An additional strand of sclerenchyma is present in the 

 most abaxial portion of the keel. Chlorenchyma occurs on the abaxial face 

 of the bract. 



5. A. lincarifoHa (fig. 60). This sepal is distinctive in the limited amount 

 of sclerenchyma present on the adaxial face. The remainder of the bract con- 

 sists of parenchyma cells which are polygonal as seen in transection. The cen- 

 tral portion of this parenchyma contains numerous chloroplasts. Five veins are 

 present in the mesophyll. 



6. A. macrostachya var. angustior (fig. 61). This sepal has sclerenchyma 

 distribution similar to that of A. linearifolia, but the adaxial band is wider 

 and is connected with at least a partial abaxial band in the wings (at levels 

 higher than that shown). Sclerenchyma is very thick-walled. Five bundles 

 are present in the non-photosynthetic parenchyma which composes the remainder 

 of the sepal. 



7. .4. macrostachya var. macrostachya. The sepal in this variety in inter- 

 mediate between those of var. angustior and var. robustior in that the abaxial 

 sclerenchyma band is better developed than in var. angustior. Some of the 

 lateral bundles are embedded in the sclerenchyma of the wings. 



8. A. macrostachya var. robustior (fig. 62). The sclerenchyma on the adaxial 

 surface is paralleled (and in places, fused with) a band which parallels the 

 abaxial surface along the wings. The abaxial sclerenchyma extends farther 

 into the keel than in the other varieties. The five bundles are present in the 

 non-photosynthetic parenchyma which comprises the remainder of the sepal. 



9. A. sprucei (fig. 63). This sepal shows two distinct zones of sclerenchyma: 

 an adaxial one which parallels the inner face of the sepal, and an abaxial zone 

 in the keel. Appproximately nine bundles are present. A narrow band of 

 chlorenchyma is present on the abaxial face of the bract. 



