OUTLINES OF BOTANt. xi 



94. Flowers are unsyimnetrical or anisomerous, strictly speaking, when any one of the whorls 

 has a different number of parts from any other ; but when the pistils alone are reduced in 

 number, the flower is still frequently called symmetrical or isomerous, if the calyx, corolla, and 

 staminal whorls have all the same number of parts. 



95. Flowers are irregular when the parts of any one of the whorls are unequal in size, 

 dissimilar in shape, or do not spread regularly round the axis at equal distances. It is however 

 more especially irregularity of the corolla that is referred to in descriptions. A slight inequality 

 in size or direction in the other whorls does not prevent the flower being classed as regular, if 

 the corolla or perianth is conspicuous and regular. 



§ 9. The Calyx and Corolla, or Perianth. 



96. The Cetlyx (90) is usually green, and smaller than the corolla ; sometimes very minute, 

 rudimentary, or wanting, sometimes very indistinctly whorled, or not whorled at all, or in two 

 whorls, or composed of a large number of sepals, of which the outer ones pass gradually into 

 bracts, and the inner ones into petals. 



97. The Corolla (90) is usually coloured, and of a more delicate texture than the calyx, 

 and, in popular language, is often more specially meant by the flower. Its petals are more rarely 

 in two whorls, or indefinite in number, and the whorl more rarely broken than in the case of 

 the calyx, at least when the plant is in a natural state. Double flowers are in most cases an 

 accidental deformity or monster in which the ordinary number of petals is multiplied by the 

 conversion of stamens, sepals, or even carpels into petals, by the division of ordinary petals, or 

 simply by the addition of supernumerary ones. Petals are also sometimes very small, rudimen- 

 tary, or entirely deficient. 



98. In very many cases, a so-called simple perianth (15) (of which the parts are usually called 

 leaves or segments) is one in which the sepals and petals are similar in form and texture, and 

 present apparently a single whorl. But if examined in the young bud, one half of the parts 

 will generally be found to be placed outside the other half, and there will frequently be some 

 slight difference in texture, size, and colour, indicating to the close observer the presence of both 

 calyx and corolla. Hence much discrepancy in descriptive works. Where one botanist 

 describes a simple perianth of six segments, another will speak of a double perianth of three 

 sepals and three petals. 



99. The following terms and prefixes, expressive of the modifications of form and arrange- 

 ment of the corolla and its petals, are equally applicable to the calyx and its sepals, and to the 

 simple perianth and its segments. 



. 100. The Corolla is said to be monopetalous when the petals are united, either entirely or at 

 the base only, into a cup, tube, or ring ; polypetalous when they are all free from the base. 

 These expressions, established by a long usage, are not strictly correct, for monopetalous 

 (consisting of a single petal) should apply rather to a corolla really reduced to a single petal, 

 which would then be on one side of the axis ; and polypetalous is sometimes used more appro- 

 priately for a corolla with an indefinite number of petals. Some modern botanists have there- 

 fore proposed the term gamopetalous for the corolla with united petals, and dialypetalous for 

 that with free petals ; but the old-established expressions are still the most generally used. 



101. When the petals are partially united, the lower entire portion of the corolla is called the 

 tube, whatever be its shape, and the free portions of the petals are called the teeth, lobes, or 

 segments (39), according as they are short or long in proportion to the whole length of the 

 corolla. When the tube is excessively short, the petals appear at first sight free, but their 

 slight union at the base must be carefully attended to, being of Importance in classification. 



102. The SSstivation of a corolla, is the arrangement of the petal^^, or of such portion of 

 them as is free, in the unexpanded bud. It is 



valvate, when they are strictly whorled in their whole length, their edges being placed 

 against each other without overlapping. If the edges are much inflexed, the sstivation is at 

 the same time induplicate ; involute, if the margins are rolled inward ; reduplicate, if the 

 margins project outwards into salient angles ; revolute, if the margins are rolled outwards ; 

 plicate, if the petals are folded in longitudinal plaits. 



imbricate, when the whorl is more or less broken by some of the petals being outside the 

 others, or by their overlapping each other at least at the top. Five-petalled imbricate corollas 

 are quincuncially imbricate when one petal Is outside, and an adjoining one wholly inside, the 

 three others intermediate and overlapping on one side ; bilabiate, when two adjoining ones are 

 inside or outside the three others. Imbricate petals are described as crumpled {corrugate) when 

 puckered irregularly in the bud. 



twisted, contorted, or convolute when each petal overlaps an adjoining one on one side, and 

 is overlapped by the other adjoining one on the other side. Some botanists include the twisted 

 ffistivation in the general term imbricate ; others carefully distinguish the one from the other. 



103. In a few cases the overlapping is so slight that the three sestivations cannot easily be 

 distinguished one from the other ; in a few others the aestivation is variable, even in the same 

 species, but, in general, it supplies a constant character in species, in genera, or even in Natural 

 Orders. 



