COROLLA. 63 



where it is pure white. The calyx is of use in protecting the other parts of the 

 flower before they expand, and afterward supporting them ia tlieir proper position. 

 Pinks having petals with long and slender claws which would droop or break with- 

 out support, have a calyx. Tulips having firm petals, and each one resting upon 

 a broad strong basis, are able to support themselves, and they have no calyx. In 

 some plants the calyx serves as a seed-vessel, as in the order Gymnospcrmia, of 

 the class Didynamia. 



LECTUEE XII. 



COROLLA. 



69. In observing the development of the plant from the cotyl- 

 edons npward, we see the leaves become gradually more per- 

 fect in their strnctm-e. When they tend toward the formation 

 of the calyx there is a contraction in the surface. The corolla 

 is produced by a new expansion or develoj)ment. The petals 

 are usually longer than the sepals, and more delicate in texture. 

 The affinity which exists between the calyx and corolla is ob- 

 vious in many plants where the calyx is partly green, partly 

 colored, as if tending to pass into a petaloid state. 



a. " The idea of petals bemg modified, or transformed leaves, seems to be further 

 corroborated by the structure of papilionaceous flowers. The greater portion of 

 the plants which bear that kind of flowers, have also pinnate leaves ; and the struc- 

 ture of those flowers presents evident indications of a similar pinnate arrangement. 

 The vexillum may be regarded as two leaflets (or pinnce) soldered by their mar- 

 gins, into one large petal, — the alee, or wings, next present an obvious pair of pin- 

 nae — and finally the keel consists of two petals more or less soldered together, 

 representing the last pair of an even-pinnate leaf, of six leaflets ; all of which are 

 thus modified and brought together into the form of a papilionaceous corolla. The 

 petals are arranged in successive pairs, the vexillum being the lowest on the recep- 

 tacle, or torus, and partially embracing others with its amplexicaul base."* 



70. Linnaeus considered the calyx as formed from the fibers 

 of the outer bark, and the corolla as a continuation of the inner 

 coat of the same. 



"The bark of the plant," says Darlington, "is the raw material from which 

 are formed and elaborated all the multiform organs or appendages to the stem 

 and branches." 



The texture of the corolla is delicate, soft, watery, and col- 

 ored ; it exhales carbonic acid gas, but not oxygen. The rich 

 and variegated colors of flowers are owing to the delicate 

 organization of the corolla ; and to this cause the transient 

 duration of this organ may also be attributed. 



a. Corollas are white, yellow, blue, violet, Ac ; in some, different colors are dcli- 

 * Dr. Darlington. 



69. Transformation of organs— a. >"tructuro of papilionaceous flawera. — 7'. Corolla— a. Color of ih9 

 corolla. 



