96 Elementary Work in Botany. 



florets. Dissect out the stamens of a large floret. How many 

 are there? Are the filaments united? Are the anthers 

 extrorse or introrse? Are there any stamens in the ray 

 flowers ? What is the use of the rays ? Of the disk corollas ? 

 Of the pappus? 



EXERCISE 50. 



\Read and discuss in the class] 



Why Flowers are in Clusters and why a Com- 

 posite Flower is the Highest Type of Inflorescence. 



We have learned that a typical flower is a stem, or its 

 upper part, in which only the lower internode, if any, is 

 developed, and the greatly modified leaves of which are in 

 four unlike sets. 



In like manner we may consider a cluster of flowers to 

 be a stem, with its branches bearing bracts and floral leaves. 

 The lower internode of the stem becomes the peduncle, and 

 that of a branch a pedicel. If all the internodes of the 

 primary stem and the first ones of the branches are 

 developed a raceme or a corymb is formed. This becomes a 

 spike if the pedicels do not grow. If the internodes above 

 the peduncle (rachis) fail to grow the raceme becomes an 

 umbel which, in turn, if the pedicels are not developed, 

 becomes a head. Evidently, then, a head, being the most 

 modified, is the highest inflorescence of the axillary type, 

 and in a similar way it can be shown that a glomerule is the 

 highest form of terminal inflorescence. 



Since plants or their parts are modified for their better- 

 ment, flowers in heads must be more effective than those in 



