SUMMARY 225 



2. A petiole, the upper part of which normally ex- 

 pands into a leaf-blade. 



In some cases, as in the Rose, all four are developed ; 

 in others one, two, or even three of these constituents 

 may remain undeveloped. 



As a general rule stipules serve to protect the bud, 

 and in most cases shelter younger leaves only ; but in 

 some, especially in quickly growing plants, as, for 

 instance, the Pea, Hop, Vine, &c., they envelop the 

 petiole and blade of their own leaf. 



In some cases the stipules of the last leaf of a year 

 protect the young leaves of the following season, as, 

 for instance, in some Magnolias, Petteria, Poplar. 



In most cases, however, these stipules drop off, and 

 the outer, covering scales are an integral part of the 

 bud. Where there are stipules, the outer leaves often 

 develop no leaf-blades (Oak, Beech, &c.). 



When stipules serve, and serve only, to protect the 

 bud, they are generally caducous, and drop off soon 

 after the leaves have expanded. 



In the Oak, Beech, Hornbeam, &c., each of these 

 outer bud-scales is a single stipule. 



In some cases, as in the Elm, Spanish Chestnut, &c., 

 each consists of the two connate stipules belonging to 

 the same leaf. 



In others, as in the Hop, each scale consists of the 

 two stipules on one side of the shoot. The two halves, 

 therefore, belong to different leaves. 



Q 



