INVOLUCKE. 



93 



nature is certainly obscme. ^ They are subject to the same laws of Tcnation and 

 form, perform the same functions, and are sometimes almost u ndistinguishable 

 from the leaves themselves. They also (very rai-ely) develop buds in their axils. 

 a. WJien they grow from the stem itself, they may, therefore, be regarded as 

 rudimentary leaves, but when from the base of the petiole, as is most common, 

 ' they are the undeveloped leaflets of a pinnate leaf, as in the rose. 



251. When leaves are furnished with stipules they are said 

 to be stipulate, and when without them they are exstipidate. 

 The stipules which are situated at the base of leaflets are called 

 stipcls. 



^ FIG. 35. — Stipules, Bracts, &c. 1, a, stipule of grass ; 2, 6, of rose ; 3, c, bract of Tilia ; 

 4, d, of a Campanula ; 5, Sium, a, involucre, c, involucel ; 6, Comus Canadensis, a, colored 

 involucre, c, flowers ; 7, Arum, a spathe, c, spadix. 



252. Bracts, called also floral leaves, are leaf-like append- 

 ages, intermediate between leaves and the floral organs. From 

 leaves they are generally distinguished by their being placeJ 

 near the flower, their smaller size, their difference in form, and 

 often in color. 



253. That bracts are of the same nature as leaves is perfectly evident, for so 

 gradual is the transition between them that no absolute limits can be assigned. 

 That they have a common origin with the sepals of the calyx also, is equally evi- 

 dent, — so imperceptibly do the latter pass into bracts; affording one of the 

 strongest proofs of the doctrine of floral metamoi-phosis. 



o. Bracts have received ditferent names, according to their aiTangement and 

 situation. They constitute an 



254. Involucre, when they are an-anged in a whorl, and sur 

 round several flowers. In the Phlox, and generally, il is gi-eeu, 

 9 



