1960] 



ANATOMY OF GUAYANA XYRIDACEAE 



75 



3. A. sprucei (fig 1 . 14). All bundles are associated with abundant scleren- 

 ehyina sheaths, with few exceptions. Such sclerenchyma may in fact incorporate 

 several bundles. Bundles that lack sheaths are frequently transversely oriented 

 and tend to delimit a cortical zone, in which leaf traces are present, from the 

 central zone. 



Orectanthe. 



As might be expected, the large stems of Orecianthe have an anatomy quite 

 distinct from that of the above species. There is a difference between the pattern 

 found in 0. ptaritepuiana (fig. 15) and that which was observed in 0. sceptrum 

 (fig. 16). In 0. ptaritepuiana, sl cortical zone is clearly delimited by a scleren- 

 chymatous cylinder which consists of lignified parenchyma cells. The inner 

 margins of this cylinder are irregular, for some bundles and their sclerenchyma- 

 tous sheaths are joined to it and others are independent in the thin-walled 

 central ground tissue. Outside of the sclerenchyma cylinder, the parenchyma 

 is also thin-walled. Bundles in this region are smaller than those within the 

 cylinder, and are either lacking in sclerenchyma sheaths or very sparingly pro- 

 vided with such tissue. In 0. sceptrum (fig. 16) the entire central portion of 

 the stem consists of lignified ground tissue. Wall thickenings are much greater 

 toward the exterior of the sclerenchymatous core. In addition, wall thickenings 

 are greater on the 2-3 layers of cells that sheath bundles in the sclerenchymatous 

 zone. The cortical region consists of non-lignified parenchyma which contains 

 vascular bundles smaller than those encased in the sclerenchyma core. These 

 leaf traces are ordinarily provided with fibrous sheaths which completely encase 

 them. 



Achlyphila. 



In the single species, prostrate rhizomatous stems are present. Upright stems 

 are formed in connection with production of inflorescences, and these are con- 

 sidered under " Inflorescence Axis" below. The stem described here, therefore, 

 is the rhizome, which differs from rosette stems of Xyris, Abolboda, and Orec- 

 tanthe in its long internodes. This rhizome (fig. 8) possesses a marked cylinder 

 of thick-walled sclereids which delimits the cortical region of thin-walled paren- 

 clryma cells. The outermost layer of this cylinder consists of cells that are, in 

 their thickening patterns and staining properties, very similar to root endo- 

 dermis cells. The occurrence of endodermis in rhizomes of monocotyledons is 

 not uncommon, and these cells should be so interpreted here. The inner margins 

 of the sclerenchyma cylinder are irregular in outline. In the central portion of 



Figs. 15, 16. Portions of transections of rosette stems, of Orectanthe, exterior at right. Fig. 

 15. 0. ptaritepuiana. Fig. 16. 0. sceptrum. Scale for figures 15 and 16 = 2 mm in 1 mm 

 divisions. Figs. 17-20. Portions of transections of inflorescence-axis bracts, exterior at 

 right. Fig. 17. Abolboda ciliata, section midway along length of bract. Fig. 18. A. 

 macrostachya var. macrostachya, section from tip of bract. Fig. 19. Same, section midway 

 along length of bract. Fig. 20. A. macrostachya var. robustior, section midway along length 

 of bract. Fig. 21. Orectanthe sceptrum, transection of a flattened sepal. Figs. 22-24. 

 Transections of bracts of inflorescence proper, taken midway along length of bract, exterior 

 face above. Fig. 22. Abolboda macrostachya var. robustior. Fig. 23. A. linearifolia. Fig. 

 24. A. americana. Scale for figures 17-24 = 2 mm in 1 mm divisions. Patterns as follows: 

 fine stippling = thick-walled sclerenchyma. coarser stippling = thin-walled sclerenchyma. 

 cross-hatched = chlorenchyma ; white in bundles = phloem; black = xylem; parenchymatous 

 ground tissue left blank. 



