148 PRACTICAL COURSE IN BOTANY 
away as soon as the leaf expands. When persistent, that is, 
enduring, they take various forms according to the purposes 
they serve. But under whatever guise they occur, their 
true nature may be recognized by their position on each side 
of the base of the petiole, and not in the azil, or angle formed 
by the leaf with the stem. (149.) 
167. Leaf attachment. — The normal use of the petiole is 
to secure a better light exposure for the leaves, but, like other 
parts, it is subject to modifications, and is often wanting 
Fie. 179.— Adnate Fria. 180. — Leaves of Fie. 181. — Leafy 
stipules of clover. smilax, showing stipular stipules of Japan 
tendrils. quince. 
altogether. In this case the leaf is said to be sessile, that is, 
seated, on the stem, and the leaf bases are designated by 
various terms descriptive of their mode of attachment. The 
meaning of these terms, when not self-explanatory, can best 
be learned by a comparison of living specimens with Figs. 
184-187. 
168. Arrangement of leaves on the stem. — The mode 
of attachment is something quite distinct from the mode of 
leaf arrangement on the stem, or phyllotary, as it is termed 
by botanists. It was seen in 148 that this takes place in two 
different ways, the alternate and opposite. These two kinds 
of arrangement represent the principal forms of leaf disposi- 
