222 ORGANOGEAPHT, 



the upper portion, evidently belongs to the calyx, instead 

 of to the thalamus as in the former instance. Such a calyx 

 is said to be calyptrate or ojperculate. When the calyx falls 

 oflf about the same time as the corolla, as in the Crowfoot 

 or Buttercup, it is called deciduous. In other cases the calyx 

 remains after the flowering is over, as in the Henbane {Jig. 444) 

 and Mallow. When the calyx is adherent or superior it is 

 necessarily 'persistent, and forms a part of the fruit, as in the 

 Quince {fig. 457), Apple, Pear, Gooseberry, Melon, and Cucumber. 

 When it is persistent and assumes a shrivelled or withered 

 appearance, as in the Campanulas, it is marcescent; 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. 456), it is termed 

 accrescent. 



2. THE COROLLA. 



The corolla is the inner envelope of the flower. It con- 

 sists of one or more whorls of leafy organs, called petals. In a 

 complete flower {fig. 419, p) it is situated between the calyx 

 and andrcecium, and is generally to be distinguished from the 

 former, as we have already seen, by its coloured nature and 

 more delicate structure. When there is but one whorl of floral 

 envelopes, as we have also before noticed, this is to be con- 

 sidered as the calyx, and the flower is then termed apetaloid. 

 The corolla is usually the most showy and conspicuous part 

 of the flower, and what in common language is termed the 

 flower. In some rare cases, however, it is green like the calyx, 

 as in certain Cobceas and 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 {Nyynphcea albet) {fig. 436); and in 

 the same plant there is also a similar transition from the petals 

 to the stamens. 



In structure the petals resemble sepals and leaves, being com- 

 posed of parenchyma, supported by veins which are chiefly 

 formed of true spiral vessels. These veins are generally re- 

 ticulat ed. The whole petal is invested by a layer of epidermis, 

 which is usually destitute of stomata, but these organs may be 

 sometimes found on the lower surface. The corolla is generally 

 smooth, although hairs occasionally occur, as in the Bomhax ; 

 when they exist they are usually coloured, as in the Buckbean, 

 and on the inner whorl of the perianth of the Iris, which cor- 

 responds 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 Wallflower {Cheiranthus) {fig. 



