99 
seasonal extremes. Fig. A of Plate XVI. shows a leaf partially 
curved, while Fig*. B is a more highly magnified view of the curva- 
ture tissue lining a secondary furrow. 
The closing of the furrows (into which the stomata open) 
prevents circulation of air in the pit-like entrances to the stomata, 
and this end is further served by the interlocking of the stout 
hairs which grow in greatest profusion at the edges of the longi- 
tudinal ridges. Finally, on rolling 1 being completed, the furrows 
themselves open on the closed cavity contained by the rolled leaf. 
There is then a most striking and successful attempt to protect 
the plant from excessive transpiration. 
On the checked transpiration allowing the plant to make good 
by absorption the undue water loss, the cells of the curvature 
tissue and the green mesophyll regain their turgor and the leaf 
unrolls. 
Reference to the structure exhibited by an oat leaf is informa- 
tive with regard to the origin of the specialised structures of the 
marram grass leaf. 
Leaf of Xanthorrfwea prei&sii. 
The long brittle, prismatic leaf of this plant is anatomically 
divided into two distinct zones. 
The outer layer, shown as a narrow border in a transverse 
section (Plate XVI 1.) contains the cldorophyll-bearing cells and 
much sclerenchyma. This latter tissue forms girders, triangular in 
section, running in the direction of the length of the leaf, the 
broad bases forming a rigid support for the epidermis. The 
outermost layer of sclerenchyma, one cell thick, is marked off from 
the remaining portion of this tissue by taking acid fuchsin stain 
more feebly, and consequently stands out as a light line between 
the epidermal layer and the cells situated more deeply. It also 
runs continuously, forming a connecting link between neighbouring 
girders of sclerenchyma. The chlorophyll -bearing cells form 
columns of palisade tissue lying between the sclerenchyma strands, 
and are crowded with polygonal chloroplastids, In the transverse 
section, the palisade tissue appears as a series of scallops around 
the margin of the leaf, each portion of it being so placed with 
respect to the sclerenchyma that the light is much tempered. The 
epidermis is composed of conical cells, the cavities being much 
encroached upon by thickenings of the cell walls. A cuticle is 
strongly developed. The stomata are well protected by clusters 
of blunt hair-like outgrowths of the epidermis. Another distinctive 
feature is the lining of the stomatal cavity by a continuation of 
the outer layer of sclerenchyma mentioned above. In this region, 
however, many of the libres are irregularly formed and fissures 
