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). (Pig. 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 FlG - 216 - " 6 leaf of a 

 the stem as just described for the 

 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 



