LEAF BLADE 235 
blade and makes connection with the twig; and a pair of small 
leaf-like appendages at the base of the petiole, known as stipules. 
The portion of the leaf at the point of contact with the twig or 
stem is called the leaf base. The leaf base is generally enlarged 
so as to form a sort of cushion by which the leaf is attached to 
the stem. 
The leaves of most plants are not typical, but have one or 
more parts lacking. The stipules are very frequently absent. 
The leaves of the Thistle, Wild Let- 
tuce, Mullein, and many other plants 
have no petioles, the blade being 
directly attached to the stem. Such 
leaves are said to be sessile (mean- 
ing sitting). (Fig. 216.) In Corn, 
Wheat, Oats, and Grasses in general 
the leaves have no petioles and the 
leaf base is much expanded and 
enwraps the stalk completely for a 
considerable distance above the node. 
A leaf base enwrapping or sheathing F16- 216. — Sessile leaf of a 
the stem as just described for the apie: 
Grass type of leaf is called a leaf sheath. At the juncture of 
the blade with the sheath in the Grass type of leaf occurs an 
outgrowth which fits closely to the stem and is known as the 
ligule or rain guard. In the Corn and some other plants of 
the Grass type small projections, known as auricles, occur at 
the base of the blade. (Fig. 217.) Leaves designated as 
perfoliate have their blades so joined around the stem that 
the stem appears to pass through the leaf as shown in 
Figure 218. 
Leaf Blade. — In general, the leaf blade is expanded into a 
broad thin structure; but all gradations exist between such forms 
and those that are thick and fleshy or even cylindrical. 
The border of the blade, called margin, may be smooth or 
quite irregular, and the character of the leaf margin is one of the 
features used in classifying plants. When the margin is smooth, 
as that of the Corn leaf, it is said to be entire. Irregular margins 
differ much in the form and depth of the indentations, as illus- 
trated in Figure 219. The margin may be cut up by many small 
notches, as the margin of the Apple leaf shown in Figure 215, or 
