GENERAL STRUCTURE 271 



Most of the common wild flowers have four kinds of 

 parts; two kinds are outer and accessory, the other two 

 are inner and essential. All these parts are usually ar- 

 ranged in whorls. (A whorl is a group of leaves or leaf- 

 like structures which arise at the same node.) In a flower 

 the innermost whorl usually forms a single structure. 



B. The Outer Parts. Generally there are one or two 

 whorls of those bright-colored leaf-shaped parts which 

 have been already called petals. They form the corolla. 

 Usually the corolla is the most conspicuous part of the 

 flower. Often, instead of being composed of entirely 

 separate petals, it is a tube or funnel-shaped structure 

 which appears to be composed of united petals, separate 

 only at the top. (See Figure 107, page 286.) 



Outside and under the petals it is usual to find a whorl 

 of those protective green parts which we have already 

 called sepals. They form the calyx. The calyx often 

 appears to be composed of more or less united sepals just 

 as the corolla appears to be composed of more or less united 

 petals. (See Figure 112, page 290.) 



All the outer parts taken together form the perianth. 

 (The word means around the flower, which expresses the 

 fact that the perianth is not an essential part of the 

 flower.) Sometimes the perianth is composed of only one 

 whorl. In such cases its parts are regarded as sepals 

 whatever their color may be, and petals are said to be 

 lacking. Sometimes there is no perianth at all. In such 

 cases the flowers are said to be naked. 



C. The Inner Parts. These are more complex than 

 the outer parts. Some flowers possess only one kind of 



