THE. FLOWER. 137 
heat, and concentrate them on the fettilised ovary, thus accelerat- 
ing its development. 
The corolla is the inner envelope of the essential organs of the 
flower. It differs generally from the calyx in being of a more 
delicate tissue. The corolla alone constitutes the flower in the 
eyes of the world generally, but to a botanist the stamens and pistil 
are the essence of the flower, for under the influence of the 
stamens the pistil produces fruit, the seeds of which will perpetuate 
the species. 
The petals are organs which, when taken together, constitute 
the corolla. They take their rise, like sepals, from modified 
leaves, a fact which is easily established. In some flowers, the 
Calycanthus, for instance, the petals are so completely shaded off 
with the sepals, that it is impossible to say where the calyx ends or 
where the corolla begins. In fact, the external divisions of these 
flowers are of a greenish hue, the internal parts being of a purple 
tint ; but it is impossible to allot the intermediate divisions to one 
of the floral envelopes more than to the other. As the petals are 
Fig. 166.—Petal of Fig. 167.—Petal of Fig. 168.—Petal of the Fig. 169.—Petal of Aconite. 
Dielytra, Fennel, Columbine. 
shaded off into the sepals, the latter into ae bracts, and the bracts 
into the leaves, we must conclude from this fact also that the 
‘petals are really modified leaves. 
Like leaves, petals offer to us very different forms and most 
varied dimensions. They are generally either linear, oblong, 
elliptical, oval, or rounded. Sometimes they are boat-shaped, 
