330 
PHYSIOLOGY. 
BOOK II. 
CHAPTER VII. 
OF THE BRACTS AND FLORAL ENVELOPES. DISENGAGEMENT 
OF CALORIC. 
The bracts, when but slightly removed from the colour and 
form of leaves, no doubt perform functions similar to those of 
the latter organs ; and, when coloured and petaloid, it may 
be presumed that they perform the same office as the corolla. 
Nothing, therefore, need be said of them separately. 
With regard to the calyx, corolla and disk, I shall chiefly 
follow Dunafs statements in his ingenious pamphlet, Sur les 
Fonctions des Orqanes fioraux colores et qlanduleux : 4to ; 
Paris, 1829. 
The calyx seems, when green, to perform the functions of 
leaves, and to serve as a protection to the petals and sexual 
organs ; when coloured, its office is undoubtedly the same as 
that of the corolla. 
The common notion of the use of the corolla is, that, inde- 
pendently of its ornamental appearance, it is a protection to 
the organs of fertilisation : but, if it is considered that the 
stamens and pistils have often acquired consistence enough to 
be able to dispense with protection before the 'petals are enough 
developed to defend them, it will become more probable that 
the protecting property of the petals, if any, is of secondary 
importance only. 
Among the many speculations to which these beautiful or- 
naments have given birth is one, that the petals and disk are 
the agents of a secretion which is destined to the nutrition of 
the anthers and young ovules. These parts are formed in 
the flower-bud long before they are finally called into action ; 
in the Almond, for example, they are visible some time before 
the spring, beneath whose influence they are destined to ex- 
pand. In that plant, just before the opening of the flower, 
