On the Behaviour during Drought of Leaves of two 
Cape Species of Passerina, with some Notes on 
their Anatomy. 
BY 
D. THODAY, M.A. (Cantab.), 
Harry Bolus Professor of Botany in the University of Cape Town. 
With thirteen Figures in the Text. 
NE of the features of the vegetation of the Cape Peninsula which 
V^/ immediately strikes the observer is the prevalence of shrubby plants 
with small, often narrow leaves. Closer observation shows that many of 
these have leaves of a strictly ericoid type, with grooves usually more or 
less filled with hairs, the stomata being confined to the epidermis lining the 
groove. These plants belong to various families. Of the numerous species 
of Erica and other genera of Ericaceae, all but a few possess leaves of this 
type. They are found also in Stilbe ericoides and S'. vestita (Verbenaceae), 
Phylica spp. (Rhamnaceae), Rhus rosmarinifolia (Anacardiaceae), Pas- 
serina filiformis and Chymococca empetroides (Thymelaeaceae), Grubbia 
rosmarinifolia (Grubbiaceae), and in several genera of Compositae, including 
Stoebe , Dispar ago, Elytropappus , and Metalasia. This list is by no means 
exhaustive. 
A fact of some interest with regard to a number of the species was 
communicated to the South African Association for the Advancement of 
Science at the meeting in Bulawayo in July, 1920, namely, that the grooves 
vary in the width of their opening with changes in the conditions. In the 
dry summer of 1920, in February and March, the leaves of Erica spp., 
Stilbe vestita , and Passerina filiformis were found with the grooves quite 
or nearly closed on plants in specially dry situations. 
In Passerina the closure of the grooves was observed more frequently 
than in the other species. This was therefore selected first for detailed 
study. 
Passerina filiformis is widely distributed in South Africa. In the 
Cape Peninsula it is very common, extending from a little above sea-level 
to at least a thousand feet on the mountain slopes. 1 
1 Bolus and Wolley-Dod : Flowering Plants and Ferns of the Cape Peninsula. Trans. 
S. African Phil. Soc., xiv, 1903, p. 315. 
[Annals of Botany, Vol. XXXV. No. CXL. October, 1921.J 
