THE FLOWER. 221 



flower-clusters in the other. Thus the heads of the Sunflower and 

 of all the so-called compound flowers (394) are centripetal, the 

 flowers expanding regularly from the margin or circumference to the 

 centre ; while the branches that bear the heads are developed in the 

 centrifugal mode, the central heads being earliest to come into blos- 

 som. This is exactly reversed in all Labiatas (plants of the Mint 

 tribe) ; where the stem grows on indefinitely, producing axillaiy 

 clusters in the form of a general raceme or spike, which blossoms 

 from below upwards ; while the flowers of each cluster form a cyme, 

 and expand in the centrifugal manner. These cymes, or cymules 

 (404), are usually close and compact, and being situated one in each 

 axil of the opposite leaves, the two together frequently form a clus- 

 ter which surrounds the stem, like a whorl or verticil (as in the 

 Catnip and Horehound) : hence such flowers are often said to be 

 whorled or verticillate, which is not really the case, as they evidently 

 all spring from the axils of the two leaves. The apparent verticil 

 of this kind is sometimes termed a Verticillastee. 



413. True whorled flowers occur only in some plants with whorled 

 leaves, as in Hippuris and the Water Milfoil. 



CHAPTER IX. 



OF THE FLOWER. 



Sect. I. Its Organs, oe Component Parts. 



414. Having glanced at the circumstances which attend and con- 

 trol the production of flowers, and considered the laws which govern 

 their arrangement, we have next to inquu-e what the flower is com- 

 posed of. 



415. The Flower (117) assumes an endless variety of forms in 

 different species, so that it is very difficult properly to define it. 

 The name was earliest applied, as it is still in popular language 

 generally applied, to the delicate and gayly colored leaves or petals, 

 so different from the sober green of the foliage. But the petals, 

 and all these bright hues, are entirely wanting in many flowers, 

 while ordinary leaves sometimes assume the brilliant coloring of the 



19* 



