[Chap. XXXII 



FLOWERS, FRUITS, AND SEEDS 



353 



are usually compact structures, with the parts in close spirals or whorls 

 ( cycles ) . In the more primitive types of flowers, floral organs are spirally 

 arranged; in the more complex types they are usually cyclic and also 

 fewer in number ( Fig. 151 ) . The best way to study flowers is first to 

 examine a few common ones critically and then to amplify these initial 

 studies by further observation of some of the hundreds of different kinds 

 available each season. 



A simple flower. The flowers of tulip and sweet pea exemplifv two 

 common forms of simple flowers. The floral organs of the tulip (Fig. 



Fig. 152. Flower, fruit, and seeds of tulip. A, vertical section through center 

 of flower; B, diagram of cyclic arrangement of the floral organs; C, enlarged 

 cross section of the pistil in which the three carpels and six of the ovules are 

 evident; D, cross section of a mature pistil in which the ovules have become 

 seeds; E, a mature fruit which has split open along the midrib of each carpel. 



152) are arranged in cycles of three at the top of the flower stalk or 

 peduncle. This end of the peduncle is slightlv enlarged and is known as 

 the receptacle. The outermost cycle of leaf-like structures growing from 

 the receptacle is the calyx, composed of three sepals. In the enlarging 

 flower bud these sepals are green. They may remain green or become 

 variously colored as the flower matures, depending upon the varietv. Ex- 

 cept for position, the next cycle is very similar to the first; its three petals 



