92 



MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



[VOL. 10 



4. A. Unearifolia. An inflorescence bract is illustrated in figure 23. The 

 abaxial epidermis is sclerified; the mesophyll is divisible into three zones, from 

 outside to inside : ehlorenchyma, non-photosynthetic parenchyma, and scle- 

 renchyma. 



5. A. macrostachya var. angusiiov. The outer portion of an inflorescence- 

 axis bract consists of spongy ehlorenchyma. The adaxial portion of the mesophyll, 

 in which veins are located, consists of non-photosynthetic parenchyma. A few 

 fibers are present on the phloem poles of larger bundles. 



5. A. macrostachya var. macrostachya. The two sections shown (figs. 18, 

 19) illustrate a great deal of difference between the median region and the 

 most apical portion of an inflorescence-axis bract. At the lower level (fig. 19), 

 the mesophyll contains sclerenchyma on the adaxial face, and a few bands of 

 such tissue on the abaxial face. Chlorenchyma and non-photosynthetic par- 

 enchyma form bands within the bract. At the highest level (fig. 18), the entire 

 mesophyll consists of thin- walled sclerenchyma. 



6. A. macrostachya var. robustior (figs. 20, 22). .The inflorescence-axis 

 bract is distinctive in that the ground tissue consists of sclerenchyma, more 

 nearly thin-walled halfway between the surfaces of the bract, which contains 

 pockets of parenchyma, possibly chlorenchyma. In addition to the main series 

 of veins, a few smaller veins are adjacent and exterior to the parenchyma 

 pockets. They have the same collateral orientation as the main veins. The 

 inflorescence bract (fig. 22) is not dissimilar in structure, although it has more 

 thick-walled sclerenchyma, definite chlorenchyma, and bundles adaxial to the 

 chlorenchyma. 



Orectanthe. 



An inflorescence-axis bract of Orectanthe sceptrum subsp. occidentalis shows 

 a notable lack of mesophyll differentiation. The entire mesophyll consists of 

 thin-walled parenchyma. Small fibrous bundle caps are present on the phloem 

 poles of the veins. Inflorescence-axis bracts of 0. ptaritepuiana showed an 

 identical structure. 



Achlyphila. 



The bracts in this plant (fig. 66) are thin, papery inflorescence bracts, not 

 entirely comparable with any of the above because of the distinctive inflores- 

 cences of this plant. The three bundles are each ensheathed with a fibrous 

 bundle sheath. 



Discussion. 



Obvious distinctive modes of bract structure occur in the taxa mentioned 

 above. The lack of mesophyll differentiation in Orectanthe and Achlyphila 

 bracts is intersting, for considerable differentiation occurs in comparable bracts 

 of Abolboda. In Abolboda, particular types of bract structure (depending at 

 least in part on the location of * the bract on the plant and the level of section 

 within a bract) suggests caution in the formulation of differences among the 

 species of Abolboda in bract anatomy. 



SEPALS 



With the exception of Achlyphila, all the taxa studied here have keeled 

 sepals. Some Xyridaceae, such as Orectanthe, have both keeled and non-keeled 



