48 



PART I. THE MORPHOLOGY OF PLANTS. 



[ 12. 



anthus and Houttynia cordata ; in the Polygonaceae they cohere by 

 both their inner and outer margins, thus forming a tube, termed 

 an ocrea, which surrounds the internode above the insertion of the 

 leaf ; when the stipules of opposite leaves cohere they form on each 

 side an interpetiolar stipule, as frequently in the Rubiaceoe and in 

 the Hop; this may also take place when there are several leaves 

 in a whorl, as in the epicalyx of certain RosaceaD. 



In some cases (e.g. Smilax) the stipules are developed in the 

 form of tendrils, and in other cases (e.g. Bobinia) as spines. 



Stipules are comparatively common in Dicotyledons ; they are 

 absent in the Coniferse ; absent in Monocotyledons, excepting the 

 Naiadacea? arid Smilax ; absent in most Pteridophyta, except the 

 Marat tiaceos among Ferns. In Tropceolum ma jus only the two 



leaves which 

 succeed the 

 cotyledons 

 have stipules. 

 The leaflets 

 of a compound 

 leaf sometimes 

 have stipules 

 at their bases, 

 as in Phaseo- 

 lus, which are 

 distinguished 

 as stipels. 

 In a leaf 



without a pe- 

 tiole it SOme- 



tunes happens 



that the leaf-base is winged in continuity with the lamina; the re- 

 sult is that the wings extend round the stem, either incompletely 

 (Fig. 29^1) when the leaf is said to be auriculate; or completely 

 (J5) when it is said to be perfoliate ; when this occurs in two 

 opposite leaves, the leaves become connate (C ; see p. 37). 



There is, in some cases, a delicate membranous ventral outgrowth on the leaf 

 at the junction of epipodium and hypopodium, termed the ligule ; it occurs in 

 Grasses (Fig. 28 A), in Selaginella and Isoetes, and in the perianth-leaves of 

 some flowers (Narcissus, Lychnis). 



FIG. 29. The insertion of sessile leaves. A Auriculate leaf of 

 Tldaspi perfoliatum. B perfoliateleaf of Btipleurum rotundifolium. 

 C connate leaves of Lonicera Caprifolium. 



The Mesopodium or Petiole is commonly, but not always, present. 



