12. THE LEAF. 



31 



folded, as in the Beech, the Elm, and the Lime. Sometimes the 

 stipules appear as teeth on the upper margin of the sheathing leaf- 

 base, as in the Rose. Occasionally the two stipules are connate, 

 that is, they are more or less united ; when they cohere by their 

 outer margins they form a single opposite stipule, opposite, that 

 is, to the leaf to which they belong, as in Astragalus ; when they 

 cohere by their inner margins they form an axillary stipule, that 

 is, a stipule in the axil of the leaf to which they belong, as in Meli- 

 anthus and Houttynia cordata ; in the Polygonacese they cohere 

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

 an ocrea, which surrounds the intemode 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 Rubiacese and in 

 the Hop ; this 

 may also take 

 place when 

 there are several 

 leaves in a 

 whorl, as in the 

 epicalyx of cer- 

 tain Rosaceae. 



In some cases 

 (e.g. Smilax) the 

 stipules are de- 

 veloped in the 

 form of tendrils, 

 and in other 

 cases (e.g. Ro- 

 binia) as spines. 



Stipules are 



comparatively common in Dicotyledons ; they are absent in the 

 Coniferse ; absent in Monocotyledons, excepting the Naiadacese and 

 Smilax ; absent in most Pteridophyta, except the Marattiaceae 

 among Ferns. In Tropoeolum majus only the two leaves which 

 succeed the cotyledons have stipules. 



The leaflets of a compound leaf sometimes have stipules at their 

 bases, as in Phaseolus, which are distinguished as stipels. 



In a leaf without a petiole it sometimes happens that the leaf- 

 base is winged in continuity with the lamina ; the result is that 

 the wings extend round the stem, either incompletely (Fig. 20 .4) 

 when the leaf is said to be auriculate ; or completely (B) when it 



FIG. 20. The insertion of sessile leaves. A Auricnlate leaf of 

 Thlaspi per/oliotum. B Perfoliate leaf of Bupleurum rotundt- 

 /olium. C Connate leaves of Lonicera Capri/oHum. 



