Rhodesian species of Fuirena, Hesperantha , and J usticia. 195 
to the dorsal side, which allows of a larger size of the water-jacket cells on the 
ventral or exposed surface. This fact, coupled with the entire absence of 
extreme cuticularization and hairy covering in the order, shows the ade- 
quacy of this simple protection. 
As Rickli 1 expressly dwells on the delicate and radially stretched walls 
of the ventral epidermis of Fuirena scirpoidea Mich., F. repens Kth., it was 
suggested that the development of this tissue, so conspicuous in F. Oedipus , 
might be a special character in the genus, but examination of the other 
species available did not bear out this hypothesis. 
In F. sub-digitata these cells are about the same size and shape as in 
many species of Scirpus , Cyperus , and Carex. In F. stricta they are 
larger and radially elongated, but not so conspicuously different as in 
F. Oedipus . In both species, however, the connexion with the bundle- 
sheath is very well marked, especially on the dorsal side, where the hypo- 
dermal ribs are better developed than in F. Oedipus , and the connecting 
colourless cells, which break away from the sheath and run up each side of 
the fibrous groups, are more numerous and larger in size. 
The larger area of leaf surface in F. Oedipus , coupled with the organiza- 
tion of the stomata for rapid transpiration, no doubt necessitates the reinforce- 
ment of the water-jacket on the exposed ventral surface. It is the only 
organization for the protection of the palisade tissue, and the very marked 
increase in the size and volume of the cells proves what a very efficient as 
well as plastic organization such an uninterrupted water reservoir must be. 
Palisade and mesophyll tissue. The former is well differentiated 
(PI. XII, Fig. 12), a fact, according to Plowman 2 , rare in the Cyperaceae, 
but also seen in F. stricta and F. sub-digitata. It is composed of one 
layer and shows a decided convergence towards the bundle-sheath (Figs. 
12-13). The mesophyll has a tendency to break down, forming the charac- 
teristic large lysigenous air-canals, which alternate with the bundles and 
are so typical of the order. Traces of diaphragms occur across these air- 
spaces in the mature leaf, but are composed of plates of mesophyll and 
show no approach to stellate form. In Carex stellulata these air-spaces 
were traced back, and it was only in the very youngest stage that the leaf 
tissue was found entire (PI. XII, P"ig. 15), and even then the area to be 
destroyed is marked by the larger intercellular spaces, resulting in a looser 
arrangement of the cells. In A. sub-digitata these canals are not present. 
They are replaced by large thin-walled cells with colourless contents, which 
show lateral connexions with the bundle-sheaths, and they no doubt reinforce 
the water-storage tissue of the leaf. The breaking down of parenchymatous 
tissue in this way may possibly be connected with rapidity of transpiration. 
In the stem the cortical parenchyma between the peripheral bundles is 
broken down, and in the leaves the mesophyll tissues are similarly affected. 
1 Rickli, 1. c. 2 Plowman, 1. c. 
