Cape Species of Passerina, with some Notes on their Anatomy . 587 
Table I. 
Weight 
Water Content. 
in grm. 
% of fresh zveight. % of dry 
Original weight, grooves closed 
6.81 
28-6 
40 
After 6 hours, grooves mostly still closed 
7*50 
35*0 
54 
After 22 hours, grooves open 
9.05 
46-2 
86 
After 48 hours, grooves open 
9 * 2 3 
47 - 2 
89 
Dry weight 
4.87 
— 
The water content of the shoot as gathered was thus surprisingly low. 
The experiment showed nevertheless that the shoot was fully able to 
recover its turgor and the leaves to open their grooves. Even the maximum 
water content of the turgid shoot was no more than 47*2 per cent. 
Range of Water Content in the Dry Season . 
Following on this experiment the fresh weights were determined of 
a large number of shoots, with precautions against loss of moisture in the 
interval between collecting and weighing (March 6, 1920); the condition 
of the leaves was noted and their dry weights found. The shoots were 
taken from bushes in a variety of situations, probably also of both forms, 
which at the time I had not realized as specific. In the driest places many 
of the plants were yellowish or brownish in colour, the insolated sides of 
twigs and even of individual leaves contrasting markedly with the opposite 
sides, which were still more or less green. 
The shoots were separated into three groups according as the leaf- 
grooves were open, closed, or open in older leaves and closed in younger 
except at the base. The range of water content in each group is given in 
the following table : 
Table II. 
Range of Water Content. 
% of fresh weight. % of dry weight. 
Grooves open 45*3~37* r 8 3~59 
Some grooves open, some closed 34 - 5 - 33*3 53-50 
Grooves closed 34- 1 ~ 2 5*7 5 2_ 35 
These figures and those in Table I show that at this season of the year 
the critical water content at which the grooves closed completely was about 
34 per cent. The water content could, however, sink farther to 26 per cent, 
(about a third of the dry weight) apparently without permanent injury 
resulting. 
This very low water content in still living vegetative shoots appears to 
be without recorded parallel. 
Cases are of course known of plants which become practically air-dry 
without injury. A very interesting example of such a plant ( Myrotkamnus 
flabellifolid) grows in cracks on exposed granite slopes in Rhodesia. In 
the dry season the leaves become plicately folded and tightly adpressed to 
one another at the tips of the twigs, while these in their turn curve inwards. 
When the rains come, leaves and branches expand again. 
