SO 



MEMOIRS- OF THE NEW YORK BOTANICAL GARDEN 



[VOL. 10 



and bundle-sheath extensions ; the remainder of the parenchyma being either 

 of globular chlorenchyma cells or collapsed parenchyma cells. 



1. A. lincarifolia (figs. 32, 33). In the basal portion of the leaf (fig. 32) 

 there is a large number of vascular bundles. These alternate with pockets of 

 collapsed tissue. Most significant is the fact that veins occur as bundle-groups. 

 Most of the veins are thus compound, and consist of 2-3 bundles. This condi- 

 tion is unique in Abolboda, and proves an exception to the statement of Solereder 

 and Meyer (1929) that the bundle-group type of construction in Xyridaceae is 

 restricted to Xyris. Each bundle in the bundle-groups is surrounded by a fibrous 

 sheath which is fused with the sheaths of neighboring bundles in the group. 

 At a higher level (fig. 33) the same type of bundle is evident. There are, as 

 described for A. ciliata, marginal hypodermal fibers, and the hypodermis other 

 than this consists of about five cell layers. Bundle-sheath extensions are present, 

 but relatively infrequent — only 1-3 may be present in a section at this level. 

 The remaining mesophyll consists of spherical chlorenchyma cells which occur 

 beside the hypodermis. Lower epidermis, and around the bundle sheaths. Meso- 

 phyll not adjacent to these areas consists of collapsed parenchyma cells. The 

 structure of leaf-tips is considered below in a separate section. 



2. A. macrostachya. The sheathing portion of the leaf of A. macrostachya 

 var. macrostachya (fig. 34) is like that described for A. linearifolia in the nature 

 of chlorophyll-free and collapsed parenchyma distribution. It is thinner, how- 

 ever, and the bundles, which are not grouped, possess massive sclerenchyma 

 bundle sheaths. At upper levels in the leaf of A. macrostachya var. robustior 

 (fig. 28) a hypodermis of 3-4 layers occurs. Bundle sheath extensions consist 

 of cells similar to the hypodermis and are present on all but the smallest veins. 

 The remaining mesophyll consists of chlorenchyma, more densely arranged to- 

 ward the adaxial surface. Only the larger veins have lignified elements in the 

 bundle sheath; these are more abundant on the abaxial faces of the bundles. 

 In comparable portions of the lamina of A. macrostachya var. macrostachya 

 and var. angustior, which are much alike in leaf anatomy, only 1-3 bundle 

 sheath extensions are present. Fibrous bundle sheaths generally are complete in 

 var. angustior, whereas they often are present only along the abaxial surface 

 of veins in var. macrostachya. In other respects the three varieties are alike. 

 Structure of the leaf tips is described below. 



3. A. yprucei (fig. 37). The sheath portion of the leaf in this species is like 

 that shown for A. macrostachya (fig. 34) and requires no further comment. 

 The upper portion of the lamina in A. sprucei (fig. 37) also shows similarity to 

 that of A. macrostachya. A hypodermis 2-5 cell layers wide is present, and no 

 marginal sclerenchyma occurs. The remaining mesophyll consists of globular 

 chlorenchyma cells which are more densely arranged beneath the hypodermis. 

 The bundle sheath of all veins, in addition to the outer layer of chlorophyll-free 

 parenchyma, consists of a massive fibrous sheath. 



4. Leaf -tip. The three species above are alike in having a .thorn-like ter- 

 minus which occupies the 1-2 mm at the leaf apex. This type of apex in itself is 

 not exceptional, nor is the fact that xylem alone without phloem composes the 

 terminal portion of the vein, for this condition has been reported in other 

 monocots (Arber, 1925). The tracheids in these species (fig. 41) tend to be 

 separated from each other by parenchyma cells. The genuinely remarkable 

 feature concerning these tracheids is the presence of very wide bands which 



