1922] ARBER—LEAVES OF FARINOSAE 85 
entiation into sheath, petiole, and limb (Rapatea longipes, fig. 24). 
A curious feature common to the leaves of various members of the 
family is their tendency to asymmetry. The leaf sheath, as 
ENGLER points out in the Pflanzenfamilien, is folded, but the 
median bundle does not occupy the trough of the fold, and the 
limb correspondingly is not of equal width on either side of the 
midrib. These features are shown in fig. 24, Rapatea longipes Spr.; 
fig. 25 A, B, R. angustifolia Spr.; and fig. 26 A, B, Cephalostemon 
affinis Koern. In the last species the sheath is peculiar, since it 
thins out markedly at the fold, which is quite remote from the 
median bundle, whose position is marked externally by a ridge of 
fibrous tissue (/) adjacent to the lower surface (fig. 26 A). This 
ridge can also be recognized in the limb (fig. 26B). The 
lacunate character of the leaf tissue in Rapatea angustifolia Spr. is 
indicated in fig. 25 C, which also shows the median bundle with 
its fibrous sheath, and the small fibrous strands which run beneath 
the epidermis. The details of the median bundle of the limb of 
Cephalostemon affinis are seen in fig. 26 C. 
Bromeliaceae 
The leaves of the Bromeliads are often of a simple type, with a 
broadly sheathing base prolonged into a linear to ovate limb. 
In some cases, however (Tillandsia usneoides L. fig. 20 A, B), 
there is a marked distinction between the sheathing leaf base and 
the limb, which has a definitely petiolar character. In other cases 
the main part of the leaf suggests a leaf base, but there is a solid 
apical region which may correspond to the limb of Tillandsia 
_ usneoides on a reduced scale (10). The figures of Aechmea gamo- 
sepala Wittm. in the Flora Brasiliensis (15) show that the foliage 
leaves in this case have an acuminate apex, while the outer perianth 
members terminate in an elongated mucro, which is probably 
equivalent to the ‘‘cornet”’ in the case of Abolboda Poarchon Seub., 
discussed in a preceding paragraph. 
Commelinaceae 
The leaves of this family differ from most of those hitherto 
considered in their very complete differentiation. They usually 
