44 
Transactions of the Boyal Society of South Africa. 
as water reservoirs, a feature much more highly developed in the grass next 
to be described. 
The mesophyll is undifferentiated, consisting entirely of compact iso- 
diametric cells containing numerous small chloroplasts. It is separated 
from the vascular bundle by a well-marked bundle sheath with strongly 
thickened walls. Each sheath cell contains three or four chloroplasts of 
much larger size than those in the mesophyll. 
Attaching each bundle to the upper and lower epidermis are longitu- 
dinal strands of thick-walled fibres with simple pits. In between the 
bundles also there are vertical plates, one or two cells thick, containing a 
few small chloroplasts only, connecting the upper with the lower epidermis. 
The bundles are collateral, and comprise vessels, tracheids, fibres, paren- 
chyma, sieve tubes and companion cells. A single bundle lies beneath each 
furrow, and one beneath each ridge. 
DiGITARIA SANGUINALIS, Var. CILIARIS. (PI. XII, fig. 2.) 
This leaf agrees with that of Erianthus Sorghum in certain respects, e. g. 
the thickness of the bundle sheath with its few larger chloroplasts, and the 
presence of longitudinal rows of large clear cells, resembling motor cells, 
but not functioning as such. The latter are, however, much larger than in 
the other grass, and here are more obviously part of the water-storage 
system of the leaf. 
This leaf shows well-marked xerophilous characters, especially in the 
large development of water-storing tissue and in the fibres and hairs. The 
upper epidermis of the leaf is multiple, its rudiments having undergone 
repeated tangential division over the main vascular bundles, producing 
longitudinal stripes of surface fibres, and two or three layers of water- 
holding cells. There are no stomata on the upper surface, the chloren- 
chyma lying deep beneath. Tangential divisions also take place on the 
lower surface, which is thickly covered with fibres, leaving only narrow 
furrows in which lie the very small stomata. These furrows, moreover, are 
urther protected by spike-like epidermal outgrowths which grow across 
them. A little special water-tissue is present at the lower surface also, 
especially below the principal bundles, where it replaces the fibres of 
Erianthus Sorghum. The bundles are of the same type in both grasses. 
