Cohesion of Floral Organs. 77 



EXERCISE 43. 



Cohesion of Floral Organs. When organs of the 

 same kind grow fast to each other they are said to cohere. 

 Adhesion is the union of unlike parts. For example: the 

 petals of a petunia cohere, and the stamens adhere to the 

 corolla. The extent of the cohesion varies from a slight 

 union, usually at the base, to a complete union from base 

 to apex. In most flowers the carpels are united to form a 

 compound pistil ; in many the sepals cohere ; in nearly as 

 many the petals; and in a much smaller number the 

 stamens are united. The united portion of calyx, corolla or 

 stamens is called the tube. The upper end of a corolla tube 

 is the throat. The distinct upper parts of sepals or petals 

 form the lobes, which in the calyx are often called teeth. 

 The border of a calyx or corolla is called the limb, which is 

 entire if the union of the floral leaves is complete ; as in 

 morning-glories and petunias. 



In describing a flower, it is not necessary to tell directly 

 whether the sepals or petals are united or distinct. When 

 we say that a pink has five long-clawed petals the statement 

 implies that they are separate. Were they united the 

 description would be : Corolla limb five-lobed, etc.* 



* Pupils in botany are often required to memorize many useless terms. Such 

 words as polypetalous or choripetalous, gamopetalous or sympetalous are not worth 

 their memory cost. They add neither to the conciseness nor the accuracy of a 

 description. " Petals united" is shorter than "corolla gamopetalous." These 

 words and many others are relics of the time when all botanists wrote their 

 descriptions in Latin. The words choripetala , sympetaltz, etc., are convenient 

 headings in systematic botany. 



