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THE AUSTRALIAN NATURALIST. 207 
DENDROBIUM LINGUIFORME. 
By Hinpa° Burier, 
Dendrobium linguiforme is generally found growing upon 
rocks in exposed positions, where it is subjected to strong sun- 
light and drying winds, and where there is a meagre water sup- 
ply. The plant is a xerophyte, and its salyouaiton to its en- 
vironment is well seen in the peculiar modification of its leaf. 
The leaves vary in length from 4 to 1 incl, are elliptical in 
shape and very thick, the surface is always rough to the touch, 
and in dry weather longitudinal furrows appear owing to the 
contraction caused by loss of water from the tissues. Most of 
the leaves, and particularly those exposed to the direct rays of 
the sun, assume a purplish red tint. 
A transverse section of a leaf shows that in structure it re- 
sembles a typical monocotyledonous stem, its bulk cousisting of 
a pith-like mass in which vascular bundles are embedded. The 
outermost layer is one, of thick-walled epidermal cells, the 
outer walls of which are very strongly cutinised, and over almost 
every cell the cutinised layer forms a short, thick, blunt pro- 
cess somewhat resembling a small hair in shape. The stomata 
are not numerous, and are sunk below the general level of the 
surface. Next is a layer of thick-walled rectangular cells some- 
what radially elongated and corresponding to the palisade tissue 
of an ordinary leaf, but in this case very little chlorophyll is pre- 
sent, and often the cells contain a purplish-red pigment which 
protects the chlorophyll-bearing cells below from excessive light. 
Below this is a large zone of parenchymatous tissue in which 
numerous vascular ‘bundles are embedded. 
Intercellular spaces, in which water is stored, are very large, 
especially towards the centre of the. leaf. The outermost layers 
of these cells constitute the chief photosynthetic tissue of the 
plant, and the innermost cells, in which starch is ppundent, fune- 
tiongas storage tissue. 
