FIELDBOOK OF ILLINOIS WILD FLOWERS 
milkweed, respectively. Common chickweed is an example of 
a plant bearing ova/ leaves, f. 
CHARACTERISTICS OF LEAF PARTS 
Tips, bases and margins of leaves are described in a number 
of ways that assist and sometimes clinch the identification of 
plants. Bases and tips may commonly be referred to as rounded 
or narrowed. Short blunt tips are called obtuse, sharp acute, 
and long sharp points acuminate. The margins of leaves or 
leaflets may be, as shown also in fig. 2, /obed, a, toothed, b, or 
entire, c. Teeth may be coarse or fine, sharp or blunt; or the 
leaf may be doubly toothed—having large teeth whose margins 
have small teeth, fig. 2c. The lobes or the teeth vary greatly. 
They may be small or large, round or pointed, deep or shallow, 
and their margins may be entire or toothed. The indentation 
between two lobes is called a sinus. 
Leaves originate as outgrowths from the sides of developing 
young stems while these are still in the bud. At the nodes or 
points of attachment for the leaves there may frequently be seen 
buds just above the leaf or above the scar left by the leaf when 
it drops. This position in the angle between leaf and stem is 
called the axi/ of the leaf, and buds developing there are axillary 
buds. 
ARRANGEMENTS OF LEAVES ON STEMS 
There are three possible arrangements for the leaves at 
the nodes. If there is one leaf at a node the arrangement 1s 
spiral, sometimes called alternate, since the leaves range round 
the stem so that no one is directly over the leaf at the node 
next below. Two leaves at a node form the arrangement called 
opposite; and three or more at a node the whorled. A whorl 
of leaves immediately below a flower or flower group 1s called 
an involucre; a secondary whorl of modified leaf structures 
above the involucre is called an involucel. 
Some or all of the leaves may be dasa/. In such case they 
spring from or near the base of the stem, and may be few and 
sessile or on long petioles, or many forming a rosette at the surface 
of the soil. 
Leaves divide into two great classes according to the length 
of time they remain on the stem. If they stay all winter, per- 
sisting until after new leaves develop, they are evergreen; how- 
ever, if they drop off in autumn they are known as deciduous. 
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