226. These distinctions between determinate and indeterminate inflorescence, between corymbs and cymes, and between the true and the false raceme and spike, were not recognized by botanists much more than half a century ago, and even now are not always attended to in descriptions. It is still usual and convenient to describe rounded or flat-topped and open ramification as _corymbose_, even when essentially cymose; also to call the reversed or false racemes or spikes by these (strictly incorrect) names. 227. =Mixed Inflorescence= is that in which the two plans are mixed or combined in compound clusters. A _mixed panicle_ is one in which, while the primary ramification is of the indeterminate order, the secondary or ultimate is wholly or partly of the determinate order. A contracted or elongated inflorescence of this sort is called a THYRSUS. Lilac and Horse-chestnut afford common examples of mixed inflorescence of this sort. When loose and open such flower-clusters are called by the general name of _Panicles_. The heads of Compositæ are centripetal; but the branches or peduncles which bear the heads are usually of centrifugal order. § 2. PARTS OR ORGANS OF THE FLOWER. 228. These were simply indicated in Section II. 16. Some parts are necessary to seed-bearing; these are _Essential Organs_, namely, the _Stamens_ and _Pistils_. Others serve for protection or for attraction, often for both. Such are the leaves of the Flower, or the _Floral Envelopes_. 229. =The Floral Envelopes=, taken together, are sometimes called the PERIANTH, also _Perigone_, in Latin form _Perigonium_. In a flower which possesses its full number of organs, the floral envelopes are of two kinds, namely, an outer circle, the CALYX, and an inner, the COROLLA. 230. =The Calyx= is commonly a circle of green or greenish leaves, but not always. It may be the most brightly colored part of the blossom. Each calyx-leaf or piece is called a SEPAL. 231. =The Corolla= is the inner circle of floral envelopes or flower-leaves, usually of delicate texture and _colored_, that is, of some other color than green. Each corolla-leaf is called a PETAL. 232. There are flowers in abundance which consist wholly of floral envelopes. Such are the so-called full _double flowers_, of which the choicer roses and camellias of the cultivator are familiar examples. In them, under the gardener's care and selection, petals have taken the place of both stamens and pistils. These are monstrous or unnatural flowers, incapable of producing seed, and subservient only to human gratification. Their common name of _double_ flowers is not a sensible one: except that it is fixed by custom, it were better to translate their Latin name, _flores pleni_, and call them _full flowers_, meaning full of leaves.