AUSTRALIAN MELALEUCAS AND THEIR ESSENTIAL OILS. 121 
data have come to light concerning it since that time 
showing that it is a rare species. The spikes of white 
downy buds and pale flowers make it an attractive shrub 
and one worthy of cultivation. 
Mueller in his description (loc. cit.) states that the leaves 
are three nerved,’’ but in this feature of venation just a 
slight point appears to have escaped his observation, viz:— 
that in some cases the leaves are six or more veined. 
(b) Histology.—A section of the leaf shows a particular 
uniformity of anatomical structure. The palisade paren- 
chyma forms a band of a single row around the leaf below 
a rather narrow epidermis. The vascular bundles are 
surrounded by xylemic or woody fibres, bounded on the 
main bundles by supporting tissue, between them and the 
dorsal and ventral epidermis of the leaf. The mesophyll or 
spongy parenchyma is composed of thin walled cells, irregu- 
larly hexagonal as seen in the section. 
A dark deposit characterises some of the sections, this 
substance being found in the lumen of the woody fibres 
surrounding the bundles, but occurring more particularly 
in the mesophyll cells bordering the parenchymatous 
palisade layers. This substance is evidently not restricted 
or deposited in any special leaf tissue of the species inves- 
tigated in this series of papers, viz:—M. thymifolia, M. 
linariifolia, M. nodosa, M. uncinata, M. bracteata, M. 
trichostachys, and M. genistifolia. It has not, however, 
been found in M. gibbosa, nor M. pauciflora, and it was 
not till after reading the first two papers that it was 
_ considered as a manganese compound. A summary of 
its occurrence in the respective Species may not be out 
of place here. Under M. uncinata will be found one of the 
finest series of microphotographs showing this substance, 
being very conspicuous in the epidermal cells, spongy par- 
enchyma, and is in such abundance in the cells surrounding 
