FLOKAL ENVELOPES — COROLLA. 



201 



On the outer surface of petals, corresponding to the lower side of 

 leaves, stomata are sometimes found. Petals are generally glabrous 

 or smooth ; but, in some instances, hairs are produced on their surface. 

 Petaline hairs, though sparse and scattered, present occasionally the 

 same arrangement as those which occur on the leaves : thus in Bom- 

 bacese they are stellate. Coloured hairs are seen 

 on the petals of Menyanthes, and on the segments 

 of the perianth of the Iris. Although petals are 

 usually very thin and delicate in their texture, they 

 occasionally become thick and fleshy, as in Stapelia 

 and Eafflesia ; or dry, as in Heaths ; or hard and 

 stiff, as in Xylopia. A petal often consists of two 

 portions — the lower narrow, resembling the petiole 

 of a leaf, and called the unguis or claw ; the upper 

 broader, like the blade of a leaf, and called the 

 lamina or Uwh. These parts are seen in the petals 

 of the Pink (fig. 305), where o is the claw, and I ^s- ^''^■ 



the limb. The claw is often wanting, as in the Rose, and the petals 

 are then sessile. Petals having a claw are unguiculate. 



Petals, properly so called, belong to Dicotyledonous plants, for in 

 Monocotyledonous the flowers consist of a perianth or perigone, which 

 is referred to the calycine envelope. Hence the venation of petals 

 resembles that of the leaves of Dicotyledons. In the claw the vessels 

 are approximated, as in the petiole, and in the limb they expand. 

 There may be a median vein whence lateral veins go ofi', at the same 

 or different heights, forming reticulations ; or there may be several 

 primary veins diverging from the base of the limb, and forming a sort 

 of fan-shaped venation. At other times the median vein divides into 

 two. 



According to the development of veins, and the growth of cellular 

 tissue, petals present varieties similar to those already noticed in the 

 case of leaves. Thus the margin is either 

 entire or divided into lobes or teeth. 

 These teeth sometimes form a regular 

 fringe round the margin, and the petal be- 

 comes fimbriated {fimbria, a fringe), as in 

 the Pink (fig. 305) ; or laciniated, as in 

 Lychnis Flos-ouculi ; or crested, as in Poly- 

 gala. Sometimes the petal becomes pinna- 

 tifid, as in Schizopetalum. The riiedian 

 vein is occasionally prolonged beyond the 



Fig. 306. 



Fig. 307. 



Fig. 805. An ungnioulate pe1al of Dianthus monspeBSUlanua. o, Unguis or claw. 

 Z, Limb, which is fimbriated, or has a fringed margin. Fig. 306. A petal of Bryngium 

 campestre, with the apex inflexed or turned down towards the base. ,,Fig. 807. A bipartite 

 petal of Stellaria media, or common Chickweed. I, The limb split into two. o. The claw. 



