XU INTRODUCTION TO BOTANY. 



Thus, a flower is, 

 dimerous, trimerous, etc., if symmetrical, according as there are 2, 

 3, etc., parts in each whorl. 



80. Flowers are UHsymmctrical, or ai/isomerous, strictly speaking, when 

 any one of the whorls has a different number of parts from the others ; 

 but when the carpels alone are reduced in number, the flower is still 

 frequently called symmetrical, or isomcrous, if the calyx, corolla, and 

 staminal whorls have all the same niunbcr of parts. 



81. Flowers are irrec/ular when the parts of any one of the whorls are 

 \mequal in size, dissimilar in shape^ or do not spread regularly round the 

 axis at equal distances. In descriptions, it is more especially irregularity 

 of the corolla that is referred to ; a slight inequality in other parts does 

 not prevent the flower being classed as regidar, if corolla or perianth be 

 regular. 



§ 10. The Perianth, and Calyx or Corolla. 



82. The Calyx or outer whorl of the perianth is usually green, smaller 

 than the corolla, and of coarser texture; sometimes very minute, rudi- 

 mentary^, or obsolete altogether ; sometimes imperfectly whorled, or not 

 whorled at all, or composed (as in Cactus) of a large ntunber of se])als, of 

 which the outer ones pass gradually into bracts, and the inner ones into 

 petals. 



83. The Corolla or inner whorl of the perianth is usually coloured, 

 larger than the calyx, and of a more delicate texture, and in popular lan- 

 guage is often called the Jloiver. Its petals, except in double Jlotoers, are 

 rarely indefinite in number, and the whorl more rarely broken than in the 

 calyx. Sometimes the petals are very small^ rudimentary, reduced to 

 scales (as in Thymelece), or absent altogether. 



84. In very many cases the so-called simple Perianth is one in which 

 the sepals and petals are nearly similar in form and texture, and present 

 apparently a single whorl. The real nature of such a perianth may be 

 detected by examining an unopened flower-bud, when one half of the 

 parts will be found placed outside of the others (as in Anthericum, Ornitho- 

 galum, Pttmex, etc.), indicating an arrangement in two whorls, or calyx 

 and corolla. Hence difi"erent authors may describe the same flower diffe- 

 rently, either as ha\'ing a single or a double perianth. 



85. In the following terms the prefixes expressive of the modifications 

 of the corolla and its petals are equally applicable to the calyx and its 

 sepals, or to the perianth and its segments. 



86. The Corolla is, 



monopetalous (sometimes called gamopetaloiis), when the petals are 

 united or soldered together, either entirely or at the base only, 

 into a cup, tube, or ring. 



polyiyetalous (or dialijH'talous), when they are all separate or f)-ee 

 from the very base. 



87. When the petals are partially united in a monopetalous corolla, the 

 low^er consolidated portion of the corolla is called the tube, whatever be its 

 shape, and the free upper portions of the petals are called the teeth, lobes, 

 or seymetits, according as they are short or long in proportion to the whole 

 length of the corolla. When the calyx or corolla enlarges after flowering 

 it is called accrescent ; when it falls early, dcciduo^is or caducous. 



88. The flat expanded portion of a petal, corresponding to the blade of 

 the leaf, is called its limb or lamina ; and the stalk, corresponding to the 

 petiole, its claw. When there is no claw, the petals are sessile. 



89. The cestivation of a corolla is the arrangement of the petals, or their 

 free portions, in an uncxpanded bud. It is ralvate, when the edges of the 

 petals touch, but do not overlap ; imbricate, when the edges overlap each 

 other, at least near the top ; twisted, contorted, or convolute, when each petal 



