Cape Species of Passerina , with some Notes on their Anatomy. 597 
development is more difficult to obtain as the fibres soon become closely 
interwoven. The clearest case found is shown in Fig. 9, b. 
In P. cf. falcifolia fibres are not found except in association with the 
vascular bundles. Nevertheless, at the free endings of the finer veins, fibres 
are found with club-shaped tips, suggesting that they have spread by similar 
hyphal growth from the larger veins (Fig. 10). 
The origin of these peculiar hyphae has not yet been observed, and 
their development requires further study. It seems not unlikely that 
hyphal growth begins at the leaf apex and that reinforcement of 
the strands of fibres in both species, as well as the formation of the 
hypodermal sheath in P. filiformis , is brought about in this way. All that 
can be definitely stated at present is that 
the hypodermal sheath is formed at a very 
early stage near the apex of the leaf. 
Most of the fibres have cellulose walls 
stainly strongly purple with chlor-zinc-iodine. 
Relatively few are stained yellow, and these 
occur scattered near the phloem (Fig. 6). 
Even these give no appreciable coloration 
with phloroglucin and hydrochloric acid, and 
only a very faint yellow with aniline sulphate. 
They are therefore only slightly lignified. 
It might be expected that the hypodermal 
fibrous sheath of P . filiformis would affect the 
closing mechanism, but I have not been able 
to obtain any evidence of this from a com- 
parison with P. cf. falcifolia. Shoots of the 
latter collected in spring transpire at first 
more rapidly than those of P. filiformis , but 
this is probably due principally to the leaves 
spreading more widely, exposing the grooves. 
The data already given, showing the close correlation between closure and 
water content in shoots collected without discriminating between the two 
species, indicate that the water content at which closure was complete 
was the same in both. The significance of the fibrous sheath is a problem, 
however, on which further evidence is required. 
Juvenile Leaves . 
Seedlings and young plants have been found belonging to P . filiformis , 
the adult leaves having the palisade layer interrupted and the hypodermal 
sheath of wandering fibres. Immediately above the cotyledons for a variable 
distance the leaves are quite different in character (Figs. 11 and 12), being 
only slightly concave, glabrous, and more or less glaucous. The lower ones 
ending freely, from shade leaf of 
P. cf. falcifolia . The strand of fibres 
projects like a brush beyond the 
vascular tissue. The club-shaped 
tips are shown on a larger scale 
in b. In a (left) two fibres show 
abortive wandering. 
