1230. The hexapetalous is a doubling of the tripetalous, corolla. There are two whorls of petals, provided the calyx has not become corolla-like in character. Both cases are demonstrable through the alternating arrangement of the parts. 1231. The number eight is a doubled four. 1232. Nine is indeed in most instances a product of three multiplied by three. 1233. The number ten is a doubled five. 1234. In every number of petals the law of unequal development consequently prevails. 1235. The original arrangement of the parts of the corolla is bilateral, and therefore symmetrical. In the papilionaceous corollæ this originally symmetrical arrangement is most perfectly maintained. They repeat the position of their pinnate leaves. 1236. This symmetrical arrangement is shown even in many tubular, as in the labiate and personate, corollæ. The trifid lower lip is the standard and wings; the bifid upper lip, on the contrary, the keel. 1237. The small liguliform petal of the lettuce's corolla is a tubular corolla entirely slit up; it is therefore mostly quinque-dentate. 1238. Corollæ which have only a single petal (the tubular-shaped corollæ should not be styled monopetalous, but those which actually have a single petal to the corolla) are indeed to be regarded for the most part as an odd leaflet; yet still much variety appears to take place in these developmental arrests. Thus here no division of the fibrous bundle was attained, or the lateral leaflets have wholly disappeared. 1239. In many this one leaflet also is arrested, and the corolla is wholly wanting. Such a corolla is to be viewed as a stem with radical, but without ramular leaves. 1240. It is not a matter of indifference whether the single involucre that is left remaining be called calyx or corolla; the distinction between both is philosophically correct, though at the same time also it may be frequently difficult to determine. Colour and relation to the stamina and fruit determine much; but respect must be also paid to the whole idea of the plant, whether it has radical leaves or not, whether the leaf-ribs do or do not ramify. Alternating stamina afford evidence of its being the corolla. COLORATION. 1241. As the colour ranges parallel with the import or quality of the matter, or since the matter and colour are of one and the same kind, so also must this hold good of the colour of the light-flower. 1242. As the corolla only, and not the calyx, is the proper light-organ, so also will it only obey the light in the coloration. 1243. The corolla can no longer be coloured green, for it is no longer a leaf. Now that which obtains another signification, which passes over into another element, must, with the function, lay aside also the old colour. The corolla is besides the perishing, fading leaf; as this begins to turn yellow or red in the autumn, so does the corolla immediately at its origin. It is a born autumnal leaf.