224 COLOURS OF FLOWERS. 



Dividing the flora into twenty parts, we may ascribe to each 

 colour, and its various tints, the following proportion : 



The analogy between the parts or petals of the corolla and 

 the leaf, is perhaps not quite so striking as between the leaf 

 and the sepals of the calyx. The phrase " rose-leaves " is an 

 expression consecrated by immemorial usage. Why not prefer 

 the term "corollary leaves or leaflets (foliola)" to that of 

 petals ? 



The corollary leaves, or petals, are organised like true leaves. 

 They have the same system of venation ; their lamina corre- 

 spond to the " limb," or " blade ;" and their unguis, or " claw," 

 to the "petiole," or stalk. (See Fig. 46, a.) 

 The upper margin of petals is frequently 

 more obtuse than the overspreading mar- 

 gin of the blade of a leaf, which, in most 

 cases, is pointed. Non-tmguiculate petals 



FIG. 46, a. Unguis of the , .. . /T ,. ,. ,\ 



Corolla. represent the sessile leaves. (Fig. 46, b.) 



FIG. 46, b. A Sessile 



Petal. Their form is much more vaned than that 



of the calicinal foliola, which are never unguiculate or petio- 

 lated. 



The petal is defined as regular when its two halves, 

 folded one upon another at the midrib, exactly cover each 

 other ; in the opposite case it is called irregular. In certain 

 species, the petals are furnished with characteristic append- 



