COROLLA. 
where it is pure white. The calyx is of use in protecting the other parts of ihe 
flower before they expand, and afterward supporting them in their 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 Gymnospermia, of 
the class Didynamia. 
LECTUEE XII. 
COEOLLA. 
69. In observing the development of the plant from the cotyl* 
edons upward, we see the leaves become gradually more per- 
fect in their structure. 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 development. The ]^etals 
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 being 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- 
UJB — 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."* 
TO. 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, <fec. ; in some, different colors are deli- 
* Dr. Darlington. 
69. Tiantformation of oro^ans — a. St ructure of papilionaceous flowers. — 7 ). Corolla— a. Celar of tb* 
•oroSla. 
