ROOTS AND STEMS. 23 



The arrangement is valvate when the edges of adjacent 

 leaves barely touch each other (Fig. 75). 



It is imbricate when the edges of the leaves overlap 

 each other (Figs. 76, 77). 



When involute leaves are applied together in a circle, 

 without overlapping (Fig. 78), they are said to be condupli* 



FIG. 73 . 



FIG. 



FIG, 75. 



FIG. 76. 



FIG. 



FIG. 78. 



FIG. 79. FIG. 80. 



FIG. 81. 



cate. When conduplicate leaves overlap each other at the 

 base (Figs. 79, 80), they are called equitant. When a con- 

 volute leaf incloses another which is rolled up in a like 

 manner (Fig. 81), the arrangement is supervolutc. 



EXERCISE X. 

 Stem and Leaves. 



The point at which, and the mode by which, a leaf is at- 

 tached to the stem is called its insertion. The first grown 

 leaves (Fig. 82) are called cotyledons (c c), and the next, 

 primordial leaves (Fig. 82, dd). Leaves are called radical 

 when they arise at or near the surface of the ground, and cau- 

 line when they grow from a stem with developed internodes. 

 The small leaves upon flower-stalks are called bracts. 



When a leaf is enlarged at its base and clasps the 

 stem, it is amplexicaul, or clasping (Fig. 83). When it 

 forms a complete sheath, as seen in Fig. 84, it is sheathing. 

 3 



