1922] ARBER—LEAVES OF FARINOSAE 83 
Xyridaceae 
This family consists of two genera, Xyris and Abolboda. Xyris, 
which includes about forty species, has a leaf with a sheathing 
base and an ensiform limb, recalling that of many members of the 
genus Iris. In Xyris Wallichii Kth. (figs. 12 A-C) and X. brevifolia 
Mich. (fig. 18 A, B) the single bundles alternate to right and left in 
the flattened limb. Fig. 18 B shows the marginal strand of Xyris 
brevifolia, which is peculiar in the possession of a conspicuous 
mass of fibers adjoining the bundle on the xylem side, whereas 
such a fibrous strand is more usually developed outside the phloem. 
As POULSEN (16) has already shown, the vascular bundles of the 
leaves of X yris may either be single or associated in groups of two 
ormore. Figs. 13 and 14 show bundle groups in the case of X. asper- 
- ata Kth. (trachyphylla Mart.) and X. anceps Lam. These bundle 
groups may attain considerable complexity; that represented in 
fig. 13.B (X. asperata) consists of nine strands imbedded in a 
common fibrous sheath. Although the flattened ensiform leaf 
type is usual in Xyris, it is not universal. PouLsEN (16) has 
figured a species (X. feretifolia Poulsen) in which the transverse 
section of the leaf limb is oval, the distance between the adaxial 
and abaxial margins being only about half as much again as the 
widt 
In Xyris the leaf epidermis is generally thick-walled. It may 
retain much the same character at the two margins as on the flanks 
of the leaf (X. Wallichii, fig. 12 C), or the elements at the margins 
may be considerably elongated, forming a fibrous border to the leaf 
(X. anceps, fig. 14 B-D). In this case the marginal elements, 
instead of standing out horizontally, slope downward, with the 
result that they are cut obliquely in transverse sections passing 
through the leaf border, which at first glance thus suggest that 
the epidermis is multi-layered in this region (fig. 14 D). 
Xyris gracilis R.Br. is significant as possessing sheathing 
leaves, in which the limb may be reduced to a mere point, and in 
which the leaf base forms practically the whole organ (fig. 17). 
These leaves may be compared with those of the second genus of 
Xyridaceae, Abolboda. I have examined the leaves of A. grandis 
