_Apetalous_, when wanting only the corolla. The case of corolla present and calyx wholly wanting is extremely rare, although there are seeming instances. In fact, a single or simple perianth is taken to be a calyx, unless the absence or abortion of a calyx can be made evident. [Illustration: Fig. 235. Flower of Mustard. 236. Its stamens and pistil separate and enlarged.] [Illustration: Fig. 237. Flower of a Violet. 238. Its calyx and corolla displayed: the five smaller parts are the sepals; the five intervening larger ones are the petals.] 252. In contradistinction to regular and symmetrical, very many flowers are _Irregular_, that is, with the members of some or all of the floral circles unequal or dissimilar, and _Unsymmetrical_, that is, when the circles of the flower or some of them differ in the number of their members. (Symmetrical and unsymmetrical are used in a different sense in some recent books, but the older use should be adhered to). Want of numerical symmetry and irregularity commonly go together; and both are common. Indeed, few flowers are entirely symmetrical beyond calyx, corolla, and perhaps stamens; and probably no irregular blossoms are quite symmetrical. 253. =Irregular and Unsymmetrical Flowers= may therefore be illustrated together, beginning with cases which are comparatively free from other complications. The blossom of Mustard, and of all the very natural family which it represents (Fig. 235, 236), is regular but unsymmetrical in the stamens. There are four equal sepals, four equal petals; but six stamens, and only two members in the pistil, which for the present may be left out of view. The want of symmetry is in the stamens. These are in two circles, an outer and an inner. The outer circle consists of two stamens only; the inner has its proper number of four. The flower of Violet, which is on the plan of five, is symmetrical in calyx, corolla, and stamens, inasmuch as each of these circles consists of five members; but it is conspicuously irregular in the corolla, one of the petals being very different from the rest. [Illustration: Fig. 239. Flower of a Larkspur. 240. Its calyx and corolla displayed; the five larger parts are the sepals; the four smaller, of two shapes, are the petals; the place of the fifth petal is vacant. 241. Diagram of the same; the place for the missing petal marked by a dotted line.] [Illustration: Fig. 242. Flower of a Monkshood. 243. Its parts displayed; five sepals, the upper forming the hood; the two lateral alike, broad and flat; the two lower small. The two pieces under the hood represent the corolla, reduced to two odd-shaped petals; in centre the numerous stamens and three pistils. 244. Diagram of the calyx and corolla; the three dotted lines in the place of missing petals.]