52 VEGETABLE ORGANOGRAPHY. 



flowering, and sometimes to the young fruit, where it is 

 persistent. It is probable, seeing the foliaceous nature 

 of this organ, that it serves also to elaborate the juices 

 destined either for the flower or the young fruit. 



Section III. 

 Of the Corolla or Petals. 



The Corolla is the more or less coloured inner en- 

 velope, which is observed in the greatest number of the 

 flowers of Dicotyledonous plants, but which is entirely 

 absent in several others. It is formed of pieces disposed 

 in one or several verticillate rows, and which bear the 

 name of Petals (petalu). 



The petals differ more in nature from leaves than the 

 calyx does, and very much resemble, as we shall see, the 

 stamens : they usually have neither stomata nor tracheae ; 

 they are of all kinds of colour, except green ; and even 

 when they are greenish, they do not appear to owe it to a 

 cause analogous to that of leaves, for they are not capable 

 of being etiolated. They do not disengage oxygen when 

 exposed to the sun, but, on the contrary, they have a ten- 

 dency to diminish the free oxygen of the air by forming 

 carbonic acid : they frequently exhale very different 

 odours from those of leaves; and these odours, when they 

 are concentrated, act in a peculiar manner upon the nerv- 

 ous system of the human species. Lastly, when they bear 

 glands or hairs, these organs are very different from those 

 of foliaceous parts. All these different characters of the 

 petals are found in the stamens and torus, and hereafter I 

 shall endeavour to prove the identity of the nature of 

 these organs. 



