226 ABOUT THE COROLLA. 



than a single floral envelope, a perianth of six foliola, of 

 which three, herbaceous and internal, alternate with three 

 petaloid and external. 



Many of our aquatic plants may be quoted as examples : 

 such as the Butomus umbellatus, or flowering rushj the little 

 frog-bit, or Hydrocharis morsus rana and the water plantain, 

 Alisma plantago. 



The tetrapdalous (or four-petalled) corolla is usually arranged 

 like a cross, and is much more frequent than the dipetalous or 

 tripetalous ; for examples, we need only refer to the large and 

 important family of the Cruciferae. 



The number five (pentapetalous) is still more common ; but 

 we meet with it in other organs besides petals, and it seems 

 particularly characteristic of the vegetable kingdom. 



Thus, all the Umbelliferse have five sepals, five petals, and 

 five stamens ; in all the Crassulaceae, the number five applies, 

 not only to the sepals and the petals, as well as to the stamens, 

 but also to the carpels which compose the ovary. 



Corollas with six, eight, nine, ten, or twelve petals are rela- 

 tively rarer; and when the petals become so numerous that 

 we cannot count them, we have to deal with transformations 

 of stamens into petals, with those monstrosities of cultivation 

 which we call double flowers, flores pleni, where all the male 

 organs have disappeared, flowers wholly unfit for fructification. 



The petals of the corolla are not always free. Like those 

 of the calyx, they may be attached to one another by their 

 edges, but this union invariably takes place, as in the former, 

 from bottom to top. Therefore, we never see any petals 



