INVOLUCRE. 95 
nature is certainly obscure. They are subject to the same laws of venation and 
form, perform the same functions, and are sometimes almost undistinguishable 
from the leaves themselves. They also (very rarely) develop buds in their axils. 
a. When they grow from the stem itself, they may, therefore, be regarded as 
rudimentary /eaves, 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 ezstipulate. 
The stipules which are situated at the base of /eajflets are called 
stipels. 
4 5 6 1 
\\ = iY Ep. ~“ 
N ——— 
FIG. 35.— Stipules, Bracts, &c. 1, a, stipule of grass; 2, b, of rose; 3, c, bract of Tilia; 
4, d, of a Campanula; 5, Sium, a, involucre, c, involucel; 6, Cornus Canadensis, a, colored 
involucre, c, flowers ; 7, Arum, @ 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 placed 
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 metamorphosis. 
a. Bracts have received different names, according to their arrangement and 
situation. They constitute an 
254. Involucre, when they are arranged in a whorl, and sur 
round several flowers. In the Phlox, and generally, it is green, 
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