VI 
portant organs we must rcter the reader to the Glossary. Leaves 
in the axils of which flower-buds are developed are called bracts; 
they are frequently of different form to the other leaves of the 
plant, and are sometimes membranaceous or scale-like. 
The leaves of most woody plants in this country drop from the 
stem in the autumn, or are deciduous; and though the Holly, Pine, 
and some other trees and shrubs retain their old leaves until the 
new ones are formed in the ensuing spring, and are consequently 
evergreen , all our trees change their leaves at some period of the 
year. 
Leaves are arranged in various ways upon the stem; but 
generally they are alternate, or situated singly at each node, on 
alternate sides of the stem, or in a spiral manner,—a mode of 
growth to which there appears to be a general tendency in plants, 
probably the result of the two movements of lateral and longi¬ 
tudinal growth proceeding at the same time at right angles to each 
other, in accordance with a well-known mechanical law. In many 
plants the leaves are opposite, or arranged in pairs on opposite sides 
of the stem; and in some they are in whorls, a number being 
situated in a circle round each node. The leaves of climbing plants 
are often furnished with elongated appendages called tendrils, by 
which they cling to the stems or other objects near them; the 
petioles in other cases twine in a similar manner, as in the Clematis 
of our hedges. 
These organs are all employed in preserving the life of the vege¬ 
table and fulfilling the various functions of its existence. Their 
form and appearance are often of great importance in botanical 
classification, particularly in distinguishing species, but must be 
considered of secondary value, as regards systematic arrangement, 
to those organs of reproduction forming the most conspicuous 
feature of the flowering plants, and upon the characters of which 
the arrangement and classification of this portion of the vegetable 
kingdom chiefly depend. 
