THE AUSTRALIAN NATURALIST. 135 
LEAF OF THE GRASSTREE (XANTHORRHA),. 
By Miss A. Brewster. 
This leaf is really more like a stem of a monocotyledonous 
type. In the presence of palisade tissue (the food factories), 
it retains its character as a leaf. 
In cross section there can be seen a mass of ground tissue, a 
pith-like mass, in which are embedded numerous veins or vas- 
cular bundles, similar to those of the maize stem. 
The most striking features of the leaf are: (1) The great 
development of the hard, strengthening tissue or Sclerenchyma, 
and (2) the seemingly constant presence of numerous crystals 
in the cells of the epidermis. 
The palisade tissue is of several layers of cells, and is in- 
terrupted by bands of sclerenchyma. It is above these bands 
that the crystals’ occur in the epidermis. There is one crystal 
in each little oblong cell, and in some eases the cell bulges out 
at the side to look somewhat like a barrel. There are lines 
of these erystal cells interrupted now and again by cells with 
no crystals present. The erystals and stomates can be seen 
by tearing off a piece of the epidermis,’ and mounting it in 
water. f 
Over the palisade bands are the stomates, and the subsidiary 
cells encircling each stomate, give the epidermis a very beauti- 
ful appearance when seen under the microscope. 
The longitudinal section shows some very interesting thick- 
enings of the cells in the sclerenchyma areas of the palisade 
zone. In the outermost layers the cells had completely lost 
their identity aS such in many cases. There remained only in- 
tensely thickened long stick-like pieces of walls with patches of 
the thicker parts dotted over with little projections of thicken- 
ing, giving them the appearance of “burrs.” 
Working inwards one ean see the cell walls getting gradually 
less thick; till only a few very tiny projecting points of 
thickening were visible. 
The leaf is a very strong xerophytic or heat-resisting type. 
This is shown by (a) the reduction of surface in the long 
narrow form, (b) the presence of palisade cells all around the 
leaf, and (c) the presence of the thickening bands. 
