[Chap. XXXII FLOWERS, FRUITS, AND SEEDS 361 



tain, wheat, and timothy has numerous flowers which are sessile, or 

 nearly so, on an erect and elongate axis. If the axis is fleshy, as in calla 

 lily and jack-in-the-pulpit, it is called a spadix. A catkin is a spike-like 

 cluster of flowers, but drooping and scaly, as in willow, cottonwood, oak, 

 hickory, and birch. When the pedicels of the individual flowers are 

 longer, as in the inflorescence of yellow toad-flax, pepper-grass, and 

 snapdragon, the arrangement is designated a raceme. Rounded or flat- 

 topped clusters of milkweed and carrot are umbels, while those of the 

 hawthorn are corymbs. The pedicels of umbels all originate in the apex 

 of a stem, whereas those of corymbs are axillary outgrowths along the 

 sides of the floral axis. If the peduncle, or floral axis, is repeatedly 

 branched, as in the inflorescence of yucca and many grasses, the cluster 

 is called a panicle. The flowers of red clover, dandelion, and sunflower 

 are sessile and grouped in a compact head. The head of flowers of 

 dahlia, daisy, cosmos, and sunflower is often mistaken for a simple flower 

 because the ray flowers have the appearance of petals and beneath them 

 is an involucre of green bracts that resembles a calyx. There are other 

 types of inflorescences, but the foregoing are the common ones, and usu- 

 ally they are not difficult to recognize. 



There are, however, many intergradations among the classified types 

 of flower clusters. Sometimes it is a matter of choice whether a particular 

 spike is short enough to be called a head, flesh v enough to be called a 

 spadix, or scaly and pendant enough to be called a catkin. In spikes, 

 racemes, and panicles the inflorescence continues to elongate at the tip 

 during the period of flowering, and it may even revert to a vegetative 

 condition as it ordinarily does in pineapple. Elongation usuallv does not 

 occur in heads, umbels, or in certain other types of inflorescences in 

 which the central terminal flower develops first. 



Flowers as forerunners of fruits. One has but to compare the pistil with 

 the mature fruit of such plants as tulip or sweet pea to see many points 

 of similarity. If successively younger fruits are examined, it soon becomes 

 evident that the fruits of these plants develop solely from the pistil or 

 from the ovulary. Such simple fruits, therefore, are merelv the result of 

 further growth of the carpels after pollination has occurred. If the stigma 

 and style wither and die, only the basal part of the carpels, the ovulary, 

 becomes the fruit. The enlarged and mature ovulary may be thin and 

 membranous, hard and thick, or soft and juicy. It encloses the seeds and 

 is often referred to as a pericarp. 



The simpler fruits of all flowering plants consist only of enlarged 



