1187. The blossom is the leaf-formation, in which the separation of the principal tissues is completely attained, where the tracheal fascicles entirely separate from the cellular substance, and become a leaf with free ribs. The cellular substance becomes the _corolla-petal_, the rib the stamen. 1188. The blossom passes through the three stages of leaf-varieties before it attains its completion, and divides therefore into three whorls, which correspond to the root-leaves, stalk-, and ramular or perfect leaves. The radical or squamose leaf appears in its repetition as _involucrum_ or _spatha_. The stalk or vascular leaf as _calyx_. The perfect or tracheal leaf as _corolla_. a. _Involucrum._ 1189. As the root puts forth numerous branches, so the involucrum or spatha frequently incloses many blossoms that constitute the thyrsus or synthetic form of inflorescence. 1190. The thyrsus or dense panicle is the whole ramage or branch-fabric repeated in the involucrum; it is therefore just as manifold as the former. 1191. The inflorescence is still as complex as the arrangement of the branches, because with every flower the ramule dies off or ceases to grow, whereby very numerous and strange relations are brought to light. 1192. The involucrum corresponds to the scale-leaves or bracts, and is therefore as a rule polypetalous. The involucral leaves stand upon a lower stage of development, are for the most part only squamose or spathiform, rarely divided or pinnate. 1193. The involucral leaves necessarily stand, as being the radical leaves of the flower, at the bottom of the peduncles or flower-stalks; each flower-stalk therefore has usually an involucral or bracteal leaf also. b. _Calyx._ 1194. The repetition of the cauline or spathe-leaf in the flower is the _Calyx_. It does not stand therefore at the base of the peduncle, but towards its summit, and is the external bud of the blossom; it is mostly spathiform, rarely or but slightly cloven, and very rarely polysepalous; it is generally green like the leaves. Although the calyx is no essential organ in itself, still it is rarely wanting and is often itself the supporter of the corolla and stamina. 1195. As the calyx is more incomplete than the corolla, so it has usually but three lobes, and if it has five, then they are frequently placed irregularly. 1196. The developmental stages of the calyx are also three. Corresponding to the scale-like leaf or bract, it is only squamiform, as in the catkins of the hazel and fir-cones; corresponding to the spathe-leaf, it is tubular or unisepalous; corresponding to the reticular leaf, it is multisepalous, and mostly deciduous.