INTRODUCTION 
off when the buds unfold in spring, though these are generally of a more 
leathery texture and may contain some chlorophyll , or green colouring- 
matter. Other reduced leaves are those produced on the flowering branches 
or inflorescence, which bear flower-buds in their axils, and serve to protect 
them. These are termed bracts ; and they vary in size, from the large 
sheathing ones, which enclose a whole inflorescence and are known as 
spathes, down to minute scales. The spathe of Narcissus is brown and 
membranous ; that of the Lords-and-ladies ( Arum maculatum ) is green or 
herbaceous. A number of bracts crowded together below an inflorescence 
are known as an involucre , as in the three leaf-like bracts of Anemone , the 
whorl of brown membranous ones in Geranium , and the imbricate series 
below the flower-head of a Daisy or other member of the great Family 
Composite. Bracts may persist in the fruit stage, as in the cup, or cupule , 
of the Acorn, and the leafy husk of the Nut. 
The usual functions of foliage-leaves are to absorb gaseous food-material, 
especially carbon-dioxide, from the air; to assimilate this material and that 
taken in by the roots, thus building up organic matter from inorganic 
materials. ; to transpire the excess of water as water-vapour, thus producing 
the upward flow of sap; and to respire , or breathe. In a few cases, such as 
our Sundews and Butterworts, the leaves also serve to digest and absorb the 
nitrogenous matter derived from captured insects: parts of leaves, or whole 
leaves, may be converted into tendrils or climbing organs ; or they may 
become protective organs as leaf-spines. 
Ordinary foliage- leaves, however, present so great a variety in 
arrangement, form, veining, surface, texture, and other characters, even 
among closely-related plants, that for descriptive purposes it is necessary to 
employ more technical terms with reference to them than to other parts of 
the plant. Onions, rushes, etc., have cylindric or centric leaves, circular 
in section : Iris and many water-side plants, liable to be occasionally 
submerged, are vertical ; but most leaves are placed more or less 
horizontally, at right angles, that is, to the direction of the incident light, 
and have a contrast in structure and in colour between their upper and 
under surfaces. Such leaves are termed dor si-ventral. A typical foliage- 
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