250 DURATION OF THE CALYX.—THE COROLLA. 
here the part which is left behind after the separation of the 
upper portion evidently belongs to the calyx, instead of to the 
thalamus, as in the former instance. In these two latter cases 
the calyx is said to be calyptrate or operculate. When the 
calyx falls off about the same time as the corolla, as in the 
Crowfoot or Buttercup, it is then called deciduous. In other 
cases the calyx remains after the flowering is over, as in the 
Henbane (jig. 461), and Mallow ; when it is described as per- 
sistent. When the calyx is adherent or superior it is neces- 
sarily persistent, and forms a part of the fruit, as in the Quince 
(fig. 473), Apple, Pear, Gooseberry, Melon, and Cucumber. 
When it is persistent and assumes a shrivelled or withered 
appearance, as in the species of Campanula, it is marcescent ; 
or, if it is persistent, and continues to grow after the flowering, 
so as to form a bladdery expansion round the fruit, as in the 
Winter Cherry, and other species of Physalis (fig. 472), it is 
termed accrescent. 
2. THE COROLLA. 
The corolla is the inner envelope of the flower. It consists 
of one or more whorls of leafy organs, called petals. In a com- 
plete flower (fig. 25, p), it is situated between the calyx and 
androecium, and is generally to be distinguished from the former, 
as we have already seen, by its coloured nature and more deli- 
cate structure. When there is but one whorl of floral envelopes, 
as we have also before noticed (page 17), this is to be considered 
as the calyx, and the flower is then termed apetaloid or mono- 
chlamydeous. The corolla is usually the most showy and con- 
spicuous part of the flower, and what in common language is 
termed the flower. In some rare cases, however, it is green like 
the calyx, asin certain Cobzas and some Asclepiadaceous plants. 
The corolla is also, in the majority of flowers which possess 
odoriferous properties, the seat of those odours. Sometimes, 
as we have seen, there is a gradual transition from the sepals 
to the petals, as in the White Water-lily (jig. 453); and in the 
same plant there is also a similar transition from the petals to 
the stamens. 
In structure the petals resemble the sepals and leaves, being 
composed of parenchyma, supported by veins which are chiefly 
formed of spiral vessels; the venation is usually reticulated. 
The whole petal is invested by epidermis, which is commonly 
destitute of stomata, but these organs may be sometimes found 
on the lower surface. The corolla is generally smooth, although 
hairs occasionally occur, as inthe Bombax ; when they exist they 
are usually coloured, as in the Buckbean, and on the inner whorl 
of the perianth of the Iris, which corresponds in position to the 
corolla. Petals are frequently narrowed below into a stalk-like 
portion, which is analogous to the petiole of a leaf, as in the 
