20 



EXSTIPULATE LEAVES 



[CH. 



other as to form a peculiar sheath or ochrea round the 

 internode above the leaf-insertion, as in Polygonum, 

 Rhubarb, and other Polygonaceae. 



While in many cases they are so small as to be easily 

 overlooked, e.g. in Barberry, Mahonia, and in the Holly, 

 where they can only be detected by microscopic examina- 

 tion in the bud; they are in others so readily cast (caducous) 

 that their existence may be unsuspected unless the student 

 examines the shoot as it emerges from the bud. This is 

 particularly the case in many Willows. Careful scrutiny 

 of the bases of young leaves with a lens will frequently 

 enable us to detect the two minute lateral scars left on 

 the fall of the stipules, just as surely as we can detect 

 those of the larger leaf-scars themselves e.g. Beech, Elm, 

 Hornbeam. The following plants have no stipules at all 

 to their leaves, which are therefore said to be exstipulate, 

 or they are so minute and fall off so early as to be practi- 

 cally absent (obsolete) : 



In the following the stipules are more or less persistent 

 and evident on the mature leaf : 



