24 



PART I. ORGANOGRAPHY. 



A leaf, when complete, 



Parts and Structure of Leaves 



consists of three parts, the 

 lamina or blade, the peti- 

 ole or leaf-stalk, and two 

 small blade-like bodies at 

 the base of the petiole called 

 the stipules. Such a leaf is 

 seen in the Tulip-tree, and 

 is illustrated in Fig. 46. Fre- 

 quently some of these parts 

 are wanting. The stipules, 

 being least serviceable to 

 the plant, are most frequent- 

 ly absent ; in this case the 

 leaf is described as exstipu- 

 late ; not uncommonly the 

 petiole is wanting and the 

 blade is inserted directly 



Upon the Stem ; it is then FlG . 4 6._Leaf of Tulip-tree, illustrating the 

 rlpcrrihprl a« cv> r c///> • «nmp- P art , s of a complete leaf. The upper part, a, is 

 OeSCnueU as Sessile , Some the l armn a, and below is the petiole, b, at the base 



times the blade is not merely of which are the two stiples - ft 

 sessile, but more or less embraces the stem at the base, when 

 it is called clasping; 

 sometimes it grows 

 quite around the stem, 

 and its edges even 

 coalesce on the oppo- 

 site side, so that the 

 stem appears to grow 

 through its base, as in 

 the Bell-wort, Fig. 47, 

 when it is described as 

 perfoliate ; sometimes, 



Fig. 47. 



Fig. 47. — Part of stem of Uvularia, illustrating perfo» 

 in the Case Of Opposite liate leaves, 

 i .1 1 Fig. 48. — Connate leaves of the Honeysuckle. 



leaves, the bases grow 



together or become coherent, apparently forming a single leaf, 

 with the stem passing through its middle, as in the Cup-plant, 

 the Boneset, and the Wood-bine or Honeysuckle, Fig. 48, in which 

 case they are called connate, and sometimes the margins of the 



