6oo Thoday . — Behaviour during Drought of the Leaves of two 
On a recently burned slope I have found juvenile shoots of P. cf. falcifolia 
growing from the bases of ojd charred stems. These, while similar in 
structure to the juvenile leaves of the seedling, often reached a much larger 
size, sometimes 2 mm. or more in width, whereas the seedling leaves do 
not exceed i mm. 
As in P. filiformis, the transition to the adult form is abrupt in respect 
of grooves, hairs, and slomatal structure. 
Cotyledons. The expanded cotyledons of P. filiformis have yet another 
type of structure. Unlike the juvenile and adult leaves, they are convex 
above, and the palisade tissue, which is feebly developed, is on the upper, 
not the under side. The stomata, on the other hand, as in the other types, 
are confined to the upper side of the cotyledons ; but they are neither raised 
nor sunl^. Cells with mucilaginous inner walls are found in both the upper 
and the lower epidermis. 
Summary. 
The structure and behaviour in drought of the ericoid leaves of two Cape 
species of Passerina , P. filiformis, Linn., and P. cf. falcifolia , C. H. Wright, 
are described. 
1. The woolly grooves are on the upper side of the leaves. As the 
water content falls in the dry summer season the edges of the leaf become 
more and more approximated until in dry situations the groove is com- 
pletely, even tightly, closed. 
2. The water content of shoots with leaf-grooves closed ranged, early 
in March, 1920, i.e. in the latter part of a very dry summer, from 34 per cent, 
down to as low as 25-7 per cent. The water content of fully turgid shoots 
at this time was only 47 per cent. At the end of the winter rainy season 
(October) the water content of shoots with new growth was about 
60 per cent. 
3. Evidence is adduced for attributing closure to cohesion forces 
developed in the outer epidermis, the cells of which are large and deep, 
and are provided with a very thick cuticle. As they contract with loss of 
water their lateral walls are thrown into bellows-like folds. 
4. The mesophyll, however, contracts in volume during closure at least 
as much as the epidermis, and the palisade tissue may show fine bellows- 
like foldings of the walls. Reasons are given for regarding water storage 
as at most a subsidiary function, of little importance in prolonged drought, 
and other advantages of a deep-celled epidermis are considered, especially 
in relation to the closing mechanism and screening from intense inso- 
lation. 
5. Anatomically, the leaves of the two species agree in most points, 
including stomata raised in the groove. They differ in the degree of 
development of the fibres, which in P . filiformis interrupt the palisade tissue 
