CHAP. II. 
CALYX. 
163 
whorls), the utility of the term Perianth is rendered ex- 
tremely confined. It is often a mere evasion of the task of 
ascertaining the exact nature of the floral envelopes in doubtful 
cases. Some writers, among whom are Link and De Can- 
dolle, have substituted Perigonium for Perianthium : but the 
latter is in most common use, its application is well under- 
stood, and there is no good reason for its being changed. 
Ehrhart, with whom the name Perigonium originated, called 
it double when the calyx and corolla are evidently distinct, 
and single if they are not distinguishable: but this use of 
terms is obsolete. 
The divisions of a calyx are called its sepals [sepala) ; a 
term first invented by Necker, and revived by De Can- 
dolle. Botanists of the school of Linnaeus call them the 
leaflets or foliola. Link says the word sepalum is barbarous, 
and proposes to substitute phylliim. The sepals are gene- 
rally longer than the corolla in aestivation, and during that 
period act as its protectors : during flowering they are mostly 
shorter. 
The calyx, in ordinary cases, if deciduous, falls off* from the 
peduncle by its base. In many cases the sepals drop off 
separately, as leaves fall from the stem ; but occasionally they 
cohere firmly into a sort of cap or lid, which is pushed off 
entire by the increase of the corolla and stamens : in these 
cases the calyx is said to be operculate, if it falls off w'ithout 
any lateral rupture of its cap, as in Eucalyptus ; and calyp- 
trate^ if at the period of falling it bursts on one side, as in 
Eschscholtzia. In the former of these two cases, the cohesion 
between the sepals is complete and never destroyed ; in the 
latter, two of the sepals separate, the cohesion betwr3en the 
remainder continuing complete. 
The calyx of Compositae is so very different in appearance 
from the calyx of other plants, that it is known by the par- 
ticular name pappus. It usually consists of hair-like pro- 
cesses proceeding from the apex of the ovary, in which case it 
is said to be pilose : if those hairs are themselves divided, it is 
plumose ; if they are very unusually stiff, it is setose^ in which 
case the setae are often reduced in number to two, or even 
one ; if the divisions of the pappus are broad and membranous, 
M 2 
