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 axil, 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 



FIG. 179. Adnate 

 stipules of clover. 



FIG. 180. Leaves of 

 smilax, showing stipular 

 tendrils. 



FIG. 181. Leafy 

 stipules of Japan 

 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 phyllotaxy, 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- 



