THE LEAF. 



49 



rest, which are often found collected at the base of flowering 

 steins of herbaceous plants, such as the Dandelion, Lettuce, Turnip, 

 Plantago (fig. 11, p. 21), &c. The ordinary leaves of the stem are 

 sometimes distinguished as cauline or stem-leaves, while the term 

 ramal is occasionally used for those on the shoots of trees and 

 shrubs when these present special characters. 



The leaves belonging to the inflorescence are called bracts. Their 

 phyllotaxis generally agrees with that of the stem-leaves. 



The point whence a leaf springs from the stem is commonly 

 called the insertion. Leaves are either articulated there, separating 

 when dead by a distinctly characterized line of fracture, or they 

 merely wither down, and leave their bases as a ragged covering to 

 the stem ; the latter condition occurs mostly in leaves with 

 sheathing bases. 



A perfect leaf is divisible into two regions (fig. 54) the blade 

 or lamina (b), and the leaf-stalk or petiole (c) ; the latter, when 

 present, may be more or less completely represented by a sheath or 

 vagina (a), partly or wholly embracing the stem from which it 

 arises. At the base of the petiole often occur distinct leaf-like 

 appendages, called stipules. All parts of the leaf blade, stalk, 

 and stipules are much subject to modification, and may even exist 

 in the forms of tendrils, spines, pitcher-like organs, &c., very unlike 



Fig. 54. 



Fig. 55. 



Diagram of the regions of a leaf : 

 a, sheath; b, blade ; c, stalk. 



A st ilked simple leaf equally 

 cordate at the base. 



regular leaves. These metamorphosed leaves, or parts of leaves, 

 are best treated of separately. 



