166 
ORGANOGRAPHY. 
BOOK I. 
7. OF the Corolla. 
88 89 90 ^ 91 
93 94 95 96 97 
That envelope of the flower which forms a second whorl 
within the calyx, and between it and the stamens, is called 
the corolla. Its divisions always, without exception, alteiv 
nate with those of the calyx, and are called petals. Like 
the sepals, they are either united by their margins, or dis- 
tinct ; but, unlike the calyx, they are rarely green, being for 
the most part either white, or of some colour, such as red, 
blue, or yellow, or of any of the hues produced by their 
intermixture. The corolla is generally also larger than the 
calyx. 
Necker called the corolla perigynandra interior.^ and Lin- 
naeus occasionally gave it the name of aulceum, a term literally 
signifying the drapery of a room. 
The alternation of the segments of the corolla with those 
of the calyx is a necessary consequence of their both being 
modifications of whorls of leaves, and therefore subject to the 
same laws of arrangement. If two whorls of leaves are 
examined, those of Galium, for example, tliey will always be 
found to be mutually so arranged, that if the internode which 
separates them were removed, they would exactly alternate 
with each other ; and as there are no known exceptions to this 
law in real leaves, it is natural that it should not be departed 
from in any modifications of them. 
