52 THE LEAF. PART I. 



well and many others. But it often happens that 

 the base is prolonged into a sort of pedicle, foot- 

 stalk, or leaf-stalk, by which the expansion is re- 

 moved to some distance from the point of attach- 

 ment, as in the leaves of the Vine and Poplar. In 

 this case the foot-stalk is denominated by botanists 

 The pe- the petiole, and the leaf said to be petiolate. (PL II. 



Fig. a.) 



Its figure. The figure of the petiole is generally semi-cylin- 

 drical, that is convex on the under surface, and flat 

 or rather channelled on the upper ; but in the leaves 

 of the Vine and Ivy it is altogether cylindrical. 

 Sometimes it is furnished with a sort of secondary 

 expansion towards the base, by which it invests the 

 stem, as in Angelica sylvestris, and then it is said to 

 be winged. Sometimes it invests the stem through- 

 out the whole of its extent, as in the Grasses, and 

 then it is denominated the sheath. Sometimes it is 

 shorter than the expansion, as in the leaf of the 

 Elm ; sometimes it is longer, as in the leaf of Con- 

 volvulus septum ; and sometimes it is of much the 

 same length with the expansion, as in the leaf of the 

 Poplar. 



Simple If the petiole supports but a single expansion it 

 is always simple, and always to be regarded as con- 

 stituting an integral part of the leaf. This identity 

 is, I believe, not generally recognized by botanists. 

 But it will require no great depth of observation to 

 convince any one that, in the case now stated, the 

 petiole and expansion constitute only one individual 



