Cape Species 0/ Passer ina, with some Notes on their Anatomy. 589 
The outer epidermis is provided with a very thick cuticle. The 
inrolling or opening of the leaf is therefore to be attributed to changes of 
volume taking place within this resistant cuticle. But it is a question 
of some importance whether changes of turgor are wholly responsible, or, 
if not, what other forces bring about the movement. 
Figs. 2 and 3 illustrate the chief structural details involved. The two 
sections represented in Fig. 2 are from old healthy leaves from ( a ) an 
ordinary sturdy plant of Passerina filiformis with more or less adpressed 
leaves, (b) an extreme shade' plant of Passerina sp.cf falcifolia , with widely 
spreading leaves. The two are in most respects very similar. The most 
conspicuous difference is in the main bundles, the fibres in (a) interrupting 
the palisade tissue and reaching the epidermis. This difference appears to 
be specific ; the continuous palisade of (b) is characteristic of the form with 
Fig. 2. Diagrams of sections of old 
healthy leaves of ( a ) P. filiformis , (b) ex- 
treme shade plant of P. cfi falcifolia. Fibres 
black ; arrangement of mesophyll cells in- 
dicated by the shading. 
Fig. 3. Part of section of leaf of P. cf. falci- 
folia. Cuticle of outer epidermis strongly 
shaded, also the raised guard cells ; f fibres ; 
vb, vascular bundles. 
spreading habit. It is shown also in Fig. 3, which is from a plant of 
this form growing in the open. 
In this figure the structure is shown more in detail. The outer 
epidermis is of relatively large cells, deeper than wide. The whole of the 
shaded part of the outer wall is strongly cutinized. The inner epidermis 
is thin, clothed with curly hairs, and has numerous raised stomata. 
To return to the question of mechanism ; experiments were made 
with sections transferred from water to 10 per cent, sodium chloride 
solution (causing plasmolysis), chloroform water, formalin, and other killing 
reagents. Plasmolysis was accompanied by only a small narrowing of the 
groove. Killing with formalin or chromacetic gave a negative or very 
slight result. With chloroform water the result varied, and this was traced 
to the direct effect of absorption of chloroform by the cuticle. A section 
Q q 
