54 VEGETABLE ORGANOGRAPHY. 



The degree of coherence of the petals, is expressed by 

 the same terms as those which refer to the calyx ; thus 

 we say of a corolla, that it is Partite when the petals 

 are united at their base ; Divided, when united as far 

 as the middle ; Dentated, when the union proceeds 

 very nearly to the apex; Entire, when the union is 

 complete. 



The petals, more frequently than the sepals, present 

 natural cohesions in their upper parts, remaining free at 

 the base ; this is seen in the two petals united at the 

 summit, which form the keel of the Papilionacese, or 

 still more in the union of the five petals in the common 

 Vine, which takes place at their summits whilst their 

 bases are distinct. They are also sometimes united by 

 their base and apex, the middle parts remaining free, as 

 in some kinds of Phyteuma. 



The petals arise, in the greatest number of cases, in a 

 single row, equal in number to the sepals, and situated 

 between each of them : when they are in two rows, the 

 external one is between the sepals, and the inner one, 

 which alternates with the first, has its petals opposite 

 the sepals : when the number of rows is more than two, 

 the third has its petals opposite those of the first, the 

 fourth opposite those of the second, &c. Among the 

 exceptions to these laws, we must mention the few cases 

 where the petals are opposite the sepals, as in the Ber- 

 beridese. 



Each petal, considered with regard to its structure, 

 sometimes presents, as leaves, a kind of support formed 

 by the union into a narrow process of all the bundles 

 which afterwards spread out to form the limb of the 

 petal ; this kind of petiole bears the name of the Claw, 

 (unguis,) and the dilated portion that of the Lamina or 

 Limb. There is a less number of unguiculate petals 

 than of petiolatc leaves. The partial bundles of vessels 



