CHAP. I. REGULAR METAMORPHOSIS. 
533 
the stem. In a specimen of a cowslip now before me, the 
calyx is formed of five perfect leaves, in no respect different 
from the others, except in being a little smaller. The 
resemblance, however, between the calyx and the stem 
leaves is often not apparent; but the identity of the calyx 
and bracts is usually more obvious. In Calycanthus, the 
transition from the one to the other is so gradual, that no one 
can say where the distinction lies ; and in numberless Ericas 
the resemblance of the bracts and calyx is perfect. The 
divisions of the calyx are also occasionally gemmiferous. A 
case is mentioned by Roper, in which one of the sepals of 
Caltha palustris was separated from the rest, and furnished with 
a bud. And Du Petit Thouars speaks of a specimen of Bras- 
sica napus, in which branches were produced within the calyx. 
I have myself a monster of Herreria 
parviflora {Jig. a), of the same na- 
ture. From this it is apparent 
that the divisions of the calyx are 
not only not distinguishable from 
bracts, but that there is often a 
strong tendency in the former to 
assume the ordinary appearance of 
leaves. There is, however, another 
point to which it is necessary to advert, in order to complete 
the proof of the identity of calyx and leaves ; this is the ver- 
ticillate arrangement of the former. 
Leaves are either opposite, alternate, or whorled; and it 
has been shown, in speaking of them, that these differences 
depend wholly upon their greater or less degree of approxi- 
mation. If the leaves of a plant are rightly considered, they 
will be found to be inserted spirally round a common axis ; 
that is to say, a line drawn from the base of the lower leaf to 
that of the one above it, thence continued to the next, and so 
on, would have a spiral direction. When leaves become 
approximated by pairs, the spire is interrupted, and the leaves 
are opposite : let the interruption be a little greater, and the 
leaves become ternate ; and if the interruption be very con- 
siderable, what is called a whorl is produced, in which several 
leaves are placed opposite to each other round a common 
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