68 



MEMOIRS' OF THE NEW YORK BOTANICAL GARDEN 



[VOL. 10 



The figure by Malme (1925) of A. vaginata shows much greater sclerifieation of 

 the vascular core than any of the species in the present study, so that this 

 species should probably be mentioned in this regard. In only a few instances 

 (Abolboda acaulis, A. americana) were relatively large phloem groups, dis- 

 tinctly alternate with xylem poles, observed. The roots studied here differ little 

 in structure of the cortex, which consists of large cells associated with relatively 

 small intercellular spaces. This condition is reported for Abolboda vaginata and 

 the species of Xyris section Xyris by Solereder and Meyer. There are, in roots 

 of Abolboda sprucei and A. americana, occasional groups of stellate parenchyma 

 cells in the cortex. This condition is mentioned by Solereder and Meyer for 

 Abolboda vaginata and a number of species of Xyris. The walls, especially the 

 inner, of the hypodermis and sometimes the adjacent walls of the subhypodermal 

 layer are thickened in all the species studied here (figs. 1,2,7). Very light thick- 

 enings were noted in the hypodermal layer of A. americana and A. macrostachya 

 var. nmcrostachya (fig. 4, upper right), Hypodermal thickenings, making pos- 

 sible the designation of an " exodermis, ' ' were noted by Solereder and Meyer 

 in Xyris indica and X. lanata. 



Abolboda. 



1. A. acaulis. Endodermal cells in this species (fig. 3) are very thick-walled, 

 with a small lumen which is nearer the outer than the inner surface of the 

 endodermis. The stele is tetrarch or pentarch ; no central vessel is present. The 

 pericycle is unbroken. 



2. A. acicularis (fig. 6). The endodermis is composed of cells only moder- 

 ately thicknened on all surfaces. The inner wall is very slightly thicker than 

 the radial or inner wall. Monarch, tetrarch, and 8-arch conditions were observed ; 

 in the last-named, a central vessel was present. Interruption of the pericycle 

 by vessels is various, and both a single and all but a single vessel in contact 

 with the endodermis were observed in different roots. 



3. A. americana (fig. 5). In all the numerous roots examined, comprising 

 several collections, the endodermis was composed of cells the inner walls of 

 which were markedly thickened. This thickening tapers on the radial walls to 

 rather thin at their juncture with the outer walls, on which no thickening is 

 present. The following stelar conditions were observed : 2-, 3-, 4-, 5-, and 6-arch. 

 All vessels are in contact with the endodermis, with the occasional exception of 

 one or two. 



4. A. linearifolia (fig. 2). The walls of the endodermal cells are thickened 

 in a U-shaped manner, but thickenings on the radial walls are tapered abruptly 

 to their point of contact with the exterior walls. A ring of parenchyma cells 

 with noticeable thickenings ensheaths the endodermis. The stele is 7- or 8-arch, 

 with one or two central vessels. Phloem groups are small and scattered ; cells of 

 the stele other than vascular elements are thick-walled. The pericycle is not 

 interrupted by vessels. 



5. A. macrostachya var. macrostachya (fig. 4). The root observed possessed 

 endodermal cells much more radially elongate than those of the preceding ones. 

 The walls are markedly thickened, with the lumen quite eccentrically placed 

 toward the exterior side of the cells. The stele is very large, and the root ob- 

 served was 15-arch, with 15 central vessels. Phloem groups are small and 

 scattered throughout the stele. The pericycle is not interrupted by vessels. 



