174 



THE LEAF 



here require attention. As to their presence or absence, leaves which 

 possess them are called Stipulate; those which do not, Exstipulate: 

 As they frequently fall with the expansion of the bud, there is great 

 danger that a stipulate plant may be mistaken for one which is not. 



As to their duration, in relation to the leaf-bud and leaf, the terms 

 caducous, deciduous, persistent, and so on, are applied to them as to 

 the parts of the perigone. 



It has been shown that the two stipules of a leaf may unite with 

 one another by either margin. They may also unite with either the 

 petiole or margin of the leaf -blade, or with the stem of the plant, in which 



Fig. 473. Cordate leaf of Nymphaca, with the margins of the sinus connate at a. 474. Inter- 

 petiolar stipules of Diodia. 475. Stipulate compound leaf, with stipellate leaflets. 



cases they are called Adnate. When leaves are opposite one another, 

 the two stipules between them may unite with one another by their 

 adjacent margins, forming the Interpetiolar Stipule (Fig. 474, a). 

 Especial importance attaches to this class of stipules, because of the 

 remarkable variation displayed in their subdivision and appendaging, 

 and the great value of their characters in generic classification in certain 

 families, especially in that highly medicinal one, the Rubiaceae. 



In some cases, the stipules so closely resemble the foliage-leaves 

 that, together with the blade, they present the appearance of a group 

 of three leaves standing side by side. In the case of opposite leaves, 

 this sometimes makes an apparent whorl of six similar leaves, or, 



